diff --git a/pri/build_opts.pri b/pri/build_opts.pri
index f332dc57a..bdb683e4a 100644
--- a/pri/build_opts.pri
+++ b/pri/build_opts.pri
@@ -40,6 +40,10 @@ else {
   DEFINES *= DEBUG=1
   gcc:QMAKE_CXXFLAGS_DEBUG *= -Wall
   clang:QMAKE_CXXFLAGS_DEBUG *= -Wall
+  msvc:QMAKE_CXXFLAGS_DEBUG *= /W4 /wd4127
+  msvc:QMAKE_CXXFLAGS_WARN_ON = ""
+  msvc:QMAKE_CXXFLAGS_DEBUG -= /W3
+  msvc:QMAKE_CXXFLAGS -= /W3
 }
 
 MOC_DIR = $$OUT_PWD/moc
diff --git a/resources/icons.qrc b/resources/icons.qrc
index 2dd52cfb9..2c39d2853 100644
--- a/resources/icons.qrc
+++ b/resources/icons.qrc
@@ -3,6 +3,7 @@
     <file>./graphics/Faenza/actions/64/application-exit.png</file>
     <file>./graphics/Faenza/actions/64/back.png</file>
     <file>./graphics/Faenza/actions/64/call-start.png</file>
+    <file>./graphics/Faenza/actions/64/dialog-no.png</file>
     <file>./graphics/Faenza/actions/64/dialog-yes.png</file>
     <file>./graphics/Faenza/actions/64/document-edit.png</file>
     <file>./graphics/Faenza/actions/64/document-export.png</file>
diff --git a/src/librssguard/core/feedsmodel.cpp b/src/librssguard/core/feedsmodel.cpp
index bb5b0c9c3..73a9ec008 100644
--- a/src/librssguard/core/feedsmodel.cpp
+++ b/src/librssguard/core/feedsmodel.cpp
@@ -389,7 +389,7 @@ QModelIndex FeedsModel::indexForItem(const RootItem* item) const {
     return QModelIndex();
   }
 
-  QStack<const RootItem*>chain;
+  QStack<const RootItem*> chain;
 
   while (item->kind() != RootItemKind::Root) {
     chain.push(item);
diff --git a/src/librssguard/core/message.cpp b/src/librssguard/core/message.cpp
index 045da982e..fd46a5483 100644
--- a/src/librssguard/core/message.cpp
+++ b/src/librssguard/core/message.cpp
@@ -14,7 +14,12 @@ Enclosure::Enclosure(QString url, QString mime) : m_url(std::move(url)), m_mimeT
 QList<Enclosure> Enclosures::decodeEnclosuresFromString(const QString& enclosures_data) {
   QList<Enclosure> enclosures;
 
-  for (const QString& single_enclosure : enclosures_data.split(ENCLOSURES_OUTER_SEPARATOR, QString::SkipEmptyParts)) {
+  for (const QString& single_enclosure : enclosures_data.split(ENCLOSURES_OUTER_SEPARATOR,
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                               Qt::SplitBehaviorFlags::SkipEmptyParts)) {
+#else
+                                                               QString::SkipEmptyParts)) {
+#endif
     Enclosure enclosure;
 
     if (single_enclosure.contains(ECNLOSURES_INNER_SEPARATOR)) {
diff --git a/src/librssguard/core/messagesmodel.cpp b/src/librssguard/core/messagesmodel.cpp
index e29e94c0a..7c75b9948 100644
--- a/src/librssguard/core/messagesmodel.cpp
+++ b/src/librssguard/core/messagesmodel.cpp
@@ -17,7 +17,7 @@
 #include <QSqlField>
 
 MessagesModel::MessagesModel(QObject* parent)
-  : QSqlQueryModel(parent), m_cache(new MessagesModelCache(this)), m_messageHighlighter(NoHighlighting),
+  : QSqlQueryModel(parent), m_cache(new MessagesModelCache(this)), m_messageHighlighter(MessageHighlighter::NoHighlighting),
   m_customDateFormat(QString()), m_selectedItem(nullptr), m_itemHeight(-1) {
   setupFonts();
   setupIcons();
@@ -286,21 +286,21 @@ QVariant MessagesModel::data(const QModelIndex& idx, int role) const {
 
     case Qt::ForegroundRole:
       switch (m_messageHighlighter) {
-        case HighlightImportant: {
+        case MessageHighlighter::HighlightImportant: {
           QModelIndex idx_important = index(idx.row(), MSG_DB_IMPORTANT_INDEX);
           QVariant dta = m_cache->containsData(idx_important.row()) ? m_cache->data(idx_important) : QSqlQueryModel::data(idx_important);
 
           return dta.toInt() == 1 ? qApp->skins()->currentSkin().m_colorPalette[Skin::PaletteColors::Highlight] : QVariant();
         }
 
-        case HighlightUnread: {
+        case MessageHighlighter::HighlightUnread: {
           QModelIndex idx_read = index(idx.row(), MSG_DB_READ_INDEX);
           QVariant dta = m_cache->containsData(idx_read.row()) ? m_cache->data(idx_read) : QSqlQueryModel::data(idx_read);
 
           return dta.toInt() == 0 ? qApp->skins()->currentSkin().m_colorPalette[Skin::PaletteColors::Highlight] : QVariant();
         }
 
-        case NoHighlighting:
+        case MessageHighlighter::NoHighlighting:
         default:
           return QVariant();
       }
diff --git a/src/librssguard/core/messagesmodel.h b/src/librssguard/core/messagesmodel.h
index 973f48b4a..176d19667 100644
--- a/src/librssguard/core/messagesmodel.h
+++ b/src/librssguard/core/messagesmodel.h
@@ -22,7 +22,7 @@ class MessagesModel : public QSqlQueryModel, public MessagesModelSqlLayer {
 
     // Enum which describes basic filtering schemes
     // for messages.
-    enum MessageHighlighter {
+    enum class MessageHighlighter {
       NoHighlighting = 100,
       HighlightUnread = 101,
       HighlightImportant = 102
diff --git a/src/librssguard/gui/dialogs/formmessagefiltersmanager.cpp b/src/librssguard/gui/dialogs/formmessagefiltersmanager.cpp
index 14d45191b..0fa2fa08d 100644
--- a/src/librssguard/gui/dialogs/formmessagefiltersmanager.cpp
+++ b/src/librssguard/gui/dialogs/formmessagefiltersmanager.cpp
@@ -23,7 +23,10 @@ FormMessageFiltersManager::FormMessageFiltersManager(FeedReader* reader, const Q
 
   GuiUtilities::applyDialogProperties(*this, qApp->icons()->fromTheme(QSL("view-list-details")));
 
+  m_ui.m_treeFeeds->setIndentation(FEEDS_VIEW_INDENTATION);
   m_ui.m_treeFeeds->setModel(m_feedsModel);
+  m_ui.m_btnCheckAll->setIcon(qApp->icons()->fromTheme(QSL("dialog-yes")));
+  m_ui.m_btnUncheckAll->setIcon(qApp->icons()->fromTheme(QSL("dialog-no")));
   m_ui.m_btnAddNew->setIcon(qApp->icons()->fromTheme(QSL("list-add")));
   m_ui.m_btnRemoveSelected->setIcon(qApp->icons()->fromTheme(QSL("list-remove")));
   m_ui.m_btnBeautify->setIcon(qApp->icons()->fromTheme(QSL("format-justify-fill")));
@@ -47,6 +50,8 @@ FormMessageFiltersManager::FormMessageFiltersManager(FeedReader* reader, const Q
     loadSelectedAccount();
     loadFilterFeedAssignments();
   });
+  connect(m_ui.m_btnCheckAll, &QPushButton::clicked, m_feedsModel, &AccountCheckModel::checkAllItems);
+  connect(m_ui.m_btnUncheckAll, &QPushButton::clicked, m_feedsModel, &AccountCheckModel::uncheckAllItems);
 
   initializeTestingMessage();
   loadFilter();
diff --git a/src/librssguard/gui/dialogs/formmessagefiltersmanager.ui b/src/librssguard/gui/dialogs/formmessagefiltersmanager.ui
index 3d9607165..c3b9217f2 100644
--- a/src/librssguard/gui/dialogs/formmessagefiltersmanager.ui
+++ b/src/librssguard/gui/dialogs/formmessagefiltersmanager.ui
@@ -77,6 +77,9 @@
            <height>150</height>
           </size>
          </property>
+         <property name="rootIsDecorated">
+          <bool>false</bool>
+         </property>
          <property name="uniformRowHeights">
           <bool>true</bool>
          </property>
@@ -88,14 +91,14 @@
        <item>
         <layout class="QVBoxLayout" name="verticalLayout">
          <item>
-          <widget class="QPushButton" name="pushButton">
+          <widget class="QPushButton" name="m_btnCheckAll">
            <property name="text">
             <string>&amp;Check all</string>
            </property>
           </widget>
          </item>
          <item>
-          <widget class="QPushButton" name="pushButton_2">
+          <widget class="QPushButton" name="m_btnUncheckAll">
            <property name="text">
             <string>&amp;Uncheck all</string>
            </property>
@@ -406,8 +409,8 @@
   <tabstop>m_btnRemoveSelected</tabstop>
   <tabstop>m_cmbAccounts</tabstop>
   <tabstop>m_treeFeeds</tabstop>
-  <tabstop>pushButton</tabstop>
-  <tabstop>pushButton_2</tabstop>
+  <tabstop>m_btnCheckAll</tabstop>
+  <tabstop>m_btnUncheckAll</tabstop>
   <tabstop>m_txtTitle</tabstop>
   <tabstop>m_txtScript</tabstop>
   <tabstop>m_btnTest</tabstop>
diff --git a/src/librssguard/gui/feedstoolbar.cpp b/src/librssguard/gui/feedstoolbar.cpp
index 32eae9272..2eb0806b7 100644
--- a/src/librssguard/gui/feedstoolbar.cpp
+++ b/src/librssguard/gui/feedstoolbar.cpp
@@ -77,10 +77,20 @@ void FeedsToolBar::loadSpecificActions(const QList<QAction*>& actions, bool init
 }
 
 QStringList FeedsToolBar::defaultActions() const {
-  return QString(GUI::FeedsToolbarActionsDef).split(',', QString::SkipEmptyParts);
+  return QString(GUI::FeedsToolbarActionsDef).split(',',
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                    Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                    QString::SkipEmptyParts);
+#endif
 }
 
 QStringList FeedsToolBar::savedActions() const {
   return qApp->settings()->value(GROUP(GUI),
-                                 SETTING(GUI::FeedsToolbarActions)).toString().split(',', QString::SkipEmptyParts);
+                                 SETTING(GUI::FeedsToolbarActions)).toString().split(',',
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                                                     Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                                                     QString::SkipEmptyParts);
+#endif
 }
diff --git a/src/librssguard/gui/feedsview.cpp b/src/librssguard/gui/feedsview.cpp
index bafffeda8..fb2fbbced 100755
--- a/src/librssguard/gui/feedsview.cpp
+++ b/src/librssguard/gui/feedsview.cpp
@@ -98,9 +98,9 @@ void FeedsView::saveExpandStates(RootItem* item) {
   QList<RootItem*> items = item->getSubTree(RootItemKind::Category | RootItemKind::ServiceRoot);
 
   // Iterate all categories and save their expand statuses.
-  for (const RootItem* item : items) {
-    const QString setting_name = item->hashCode();
-    QModelIndex source_index = sourceModel()->indexForItem(item);
+  for (const RootItem* it : items) {
+    const QString setting_name = it->hashCode();
+    QModelIndex source_index = sourceModel()->indexForItem(it);
     QModelIndex visible_index = model()->mapFromSource(source_index);
 
     settings->setValue(GROUP(CategoriesExpandStates),
diff --git a/src/librssguard/gui/messagestoolbar.cpp b/src/librssguard/gui/messagestoolbar.cpp
index 94df2e0d4..494dc72dd 100644
--- a/src/librssguard/gui/messagestoolbar.cpp
+++ b/src/librssguard/gui/messagestoolbar.cpp
@@ -118,11 +118,11 @@ void MessagesToolBar::initializeSearchBox() {
 void MessagesToolBar::initializeHighlighter() {
   m_menuMessageHighlighter = new QMenu(tr("Menu for highlighting messages"), this);
   m_menuMessageHighlighter->addAction(qApp->icons()->fromTheme(QSL("mail-mark-read")),
-                                      tr("No extra highlighting"))->setData(QVariant::fromValue(MessagesModel::NoHighlighting));
+                                      tr("No extra highlighting"))->setData(QVariant::fromValue(MessagesModel::MessageHighlighter::NoHighlighting));
   m_menuMessageHighlighter->addAction(qApp->icons()->fromTheme(QSL("mail-mark-unread")),
-                                      tr("Highlight unread messages"))->setData(QVariant::fromValue(MessagesModel::HighlightUnread));
+                                      tr("Highlight unread messages"))->setData(QVariant::fromValue(MessagesModel::MessageHighlighter::HighlightUnread));
   m_menuMessageHighlighter->addAction(qApp->icons()->fromTheme(QSL("mail-mark-important")),
-                                      tr("Highlight important messages"))->setData(QVariant::fromValue(MessagesModel::HighlightImportant));
+                                      tr("Highlight important messages"))->setData(QVariant::fromValue(MessagesModel::MessageHighlighter::HighlightImportant));
   m_btnMessageHighlighter = new QToolButton(this);
   m_btnMessageHighlighter->setToolTip(tr("Display all messages"));
   m_btnMessageHighlighter->setMenu(m_menuMessageHighlighter);
@@ -138,12 +138,20 @@ void MessagesToolBar::initializeHighlighter() {
 }
 
 QStringList MessagesToolBar::defaultActions() const {
-  return QString(GUI::MessagesToolbarDefaultButtonsDef).split(',',
-                                                              QString::SkipEmptyParts);
+  return QString(GUI::MessagesToolbarDefaultButtonsDef).split(QL1C(','),
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                              Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                              QString::SplitBehavior::SkipEmptyParts);
+#endif
 }
 
 QStringList MessagesToolBar::savedActions() const {
   return qApp->settings()->value(GROUP(GUI),
-                                 SETTING(GUI::MessagesToolbarDefaultButtons)).toString().split(',',
-                                                                                               QString::SkipEmptyParts);
+                                 SETTING(GUI::MessagesToolbarDefaultButtons)).toString().split(QL1C(','),
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                                                               Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                                                               QString::SplitBehavior::SkipEmptyParts);
+#endif
 }
diff --git a/src/librssguard/gui/statusbar.cpp b/src/librssguard/gui/statusbar.cpp
index cc82b8f9d..de791b8a0 100644
--- a/src/librssguard/gui/statusbar.cpp
+++ b/src/librssguard/gui/statusbar.cpp
@@ -73,11 +73,22 @@ void StatusBar::saveChangeableActions(const QStringList& actions) {
 }
 
 QStringList StatusBar::defaultActions() const {
-  return QString(GUI::StatusbarActionsDef).split(',', QString::SkipEmptyParts);
+  return QString(GUI::StatusbarActionsDef).split(',',
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                 Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                 QString::SkipEmptyParts);
+#endif
 }
 
 QStringList StatusBar::savedActions() const {
-  return qApp->settings()->value(GROUP(GUI), SETTING(GUI::StatusbarActions)).toString().split(',', QString::SkipEmptyParts);
+  return qApp->settings()->value(GROUP(GUI),
+                                 SETTING(GUI::StatusbarActions)).toString().split(',',
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                                                  Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                                                  QString::SkipEmptyParts);
+#endif
 }
 
 QList<QAction*> StatusBar::getSpecificActions(const QStringList& actions) {
diff --git a/src/librssguard/gui/tabbar.cpp b/src/librssguard/gui/tabbar.cpp
index 00d909686..9858e1531 100644
--- a/src/librssguard/gui/tabbar.cpp
+++ b/src/librssguard/gui/tabbar.cpp
@@ -72,17 +72,17 @@ void TabBar::wheelEvent(QWheelEvent* event) {
 
   // Make sure rotating works.
   if (number_of_tabs > 1) {
-    if (event->delta() > 0) {
+    if (event->angleDelta().y() > 0) {
       // Scroll to the LEFT tab.
-      setCurrentIndex(current_index == 0 ?
-                      number_of_tabs - 1 :
-                      current_index - 1);
+      setCurrentIndex(current_index == 0
+                      ? number_of_tabs - 1
+                      : current_index - 1);
     }
-    else if (event->delta() < 0) {
+    else if (event->angleDelta().y() < 0) {
       // Scroll to the RIGHT tab.
-      setCurrentIndex(current_index == number_of_tabs - 1 ?
-                      0 :
-                      current_index + 1);
+      setCurrentIndex(current_index == number_of_tabs - 1
+                      ? 0
+                      : current_index + 1);
     }
   }
 }
diff --git a/src/librssguard/miscellaneous/application.cpp b/src/librssguard/miscellaneous/application.cpp
index 6981eef04..29cfe240e 100755
--- a/src/librssguard/miscellaneous/application.cpp
+++ b/src/librssguard/miscellaneous/application.cpp
@@ -489,7 +489,7 @@ void Application::onAboutToQuit() {
     finish();
     qDebug("Killing local peer connection to allow another instance to start.");
 
-    if (QProcess::startDetached(QString("\"") + QDir::toNativeSeparators(applicationFilePath()) + QString("\""))) {
+    if (QProcess::startDetached(QDir::toNativeSeparators(applicationFilePath()), {})) {
       qDebug("New application instance was started.");
     }
     else {
diff --git a/src/librssguard/miscellaneous/databasefactory.cpp b/src/librssguard/miscellaneous/databasefactory.cpp
index 1ec87fca2..3b05df7b6 100644
--- a/src/librssguard/miscellaneous/databasefactory.cpp
+++ b/src/librssguard/miscellaneous/databasefactory.cpp
@@ -218,7 +218,12 @@ QSqlDatabase DatabaseFactory::sqliteInitializeInMemoryDatabase() {
                qPrintable(APP_SQL_PATH));
       }
 
-      const QStringList statements = QString(file_init.readAll()).split(APP_DB_COMMENT_SPLIT, QString::SkipEmptyParts);
+      const QStringList statements = QString(file_init.readAll()).split(APP_DB_COMMENT_SPLIT,
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                                        Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                                        QString::SkipEmptyParts);
+#endif
 
       database.transaction();
 
@@ -327,7 +332,12 @@ QSqlDatabase DatabaseFactory::sqliteInitializeFileBasedDatabase(const QString& c
                qPrintable(APP_SQL_PATH));
       }
 
-      const QStringList statements = QString(file_init.readAll()).split(APP_DB_COMMENT_SPLIT, QString::SkipEmptyParts);
+      const QStringList statements = QString(file_init.readAll()).split(APP_DB_COMMENT_SPLIT,
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                                        Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                                        QString::SkipEmptyParts);
+#endif
 
       database.transaction();
 
@@ -407,7 +417,12 @@ bool DatabaseFactory::sqliteUpdateDatabaseSchema(const QSqlDatabase& database, c
       qFatal("Updating of database schema failed. File '%s' cannot be opened.", qPrintable(QDir::toNativeSeparators(update_file_name)));
     }
 
-    const QStringList statements = QString(update_file_handle.readAll()).split(APP_DB_COMMENT_SPLIT, QString::SkipEmptyParts);
+    const QStringList statements = QString(update_file_handle.readAll()).split(APP_DB_COMMENT_SPLIT,
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                                               Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                                               QString::SkipEmptyParts);
+#endif
 
     for (const QString& statement : statements) {
       QSqlQuery query = database.exec(statement);
@@ -447,7 +462,12 @@ bool DatabaseFactory::mysqlUpdateDatabaseSchema(const QSqlDatabase& database,
       qFatal("Updating of database schema failed. File '%s' cannot be opened.", qPrintable(QDir::toNativeSeparators(update_file_name)));
     }
 
-    QStringList statements = QString(update_file_handle.readAll()).split(APP_DB_COMMENT_SPLIT, QString::SkipEmptyParts);
+    QStringList statements = QString(update_file_handle.readAll()).split(APP_DB_COMMENT_SPLIT,
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                                         Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                                         QString::SkipEmptyParts);
+#endif
 
     for (QString statement : statements) {
       QSqlQuery query = database.exec(statement.replace(APP_DB_NAME_PLACEHOLDER, db_name));
@@ -676,7 +696,12 @@ QSqlDatabase DatabaseFactory::mysqlInitializeDatabase(const QString& connection_
                qPrintable(APP_SQL_PATH));
       }
 
-      const QStringList statements = QString(file_init.readAll()).split(APP_DB_COMMENT_SPLIT, QString::SkipEmptyParts);
+      const QStringList statements = QString(file_init.readAll()).split(APP_DB_COMMENT_SPLIT,
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                                        Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                                        QString::SkipEmptyParts);
+#endif
 
       database.transaction();
 
diff --git a/src/librssguard/miscellaneous/iofactory.cpp b/src/librssguard/miscellaneous/iofactory.cpp
index a8587377e..f78ac755b 100755
--- a/src/librssguard/miscellaneous/iofactory.cpp
+++ b/src/librssguard/miscellaneous/iofactory.cpp
@@ -10,6 +10,7 @@
 #include <QFile>
 #include <QFileInfo>
 #include <QObject>
+#include <QProcess>
 #include <QTemporaryFile>
 
 IOFactory::IOFactory() = default;
@@ -70,6 +71,18 @@ QString IOFactory::filterBadCharsFromFilename(const QString& name) {
   return value;
 }
 
+bool IOFactory::startProcessDetached(const QString& program, const QStringList& arguments,
+                                     const QString& native_arguments, const QString& working_directory) {
+  QProcess process;
+
+  process.setProgram(program);
+  process.setArguments(arguments);
+  process.setNativeArguments(native_arguments);
+  process.setWorkingDirectory(working_directory);
+
+  return process.startDetached(nullptr);
+}
+
 QByteArray IOFactory::readFile(const QString& file_path) {
   QFile input_file(file_path);
   QByteArray input_data;
diff --git a/src/librssguard/miscellaneous/iofactory.h b/src/librssguard/miscellaneous/iofactory.h
index bcd41a76d..a3dd426e5 100644
--- a/src/librssguard/miscellaneous/iofactory.h
+++ b/src/librssguard/miscellaneous/iofactory.h
@@ -27,6 +27,10 @@ class IOFactory {
 
     // Filters out shit characters from filename.
     static QString filterBadCharsFromFilename(const QString& name);
+    static bool startProcessDetached(const QString& program,
+                                     const QStringList& arguments,
+                                     const QString& native_arguments = {},
+                                     const QString& working_directory = {});
 
     // Returns contents of a file.
     // Throws exception when no such file exists.
diff --git a/src/librssguard/miscellaneous/simplecrypt/simplecrypt.cpp b/src/librssguard/miscellaneous/simplecrypt/simplecrypt.cpp
index cd8050e27..5dd1ea909 100644
--- a/src/librssguard/miscellaneous/simplecrypt/simplecrypt.cpp
+++ b/src/librssguard/miscellaneous/simplecrypt/simplecrypt.cpp
@@ -31,6 +31,7 @@
 #include <QCryptographicHash>
 #include <QDataStream>
 #include <QDateTime>
+#include <QRandomGenerator>
 #include <QtDebug>
 #include <QtGlobal>
 
@@ -38,16 +39,13 @@ SimpleCrypt::SimpleCrypt() :
   m_key(0),
   m_compressionMode(CompressionAlways),
   m_protectionMode(ProtectionHash),
-  m_lastError(ErrorNoError) {
-  qsrand(uint(QDateTime::currentMSecsSinceEpoch() & 0xFFFF));
-}
+  m_lastError(ErrorNoError) {}
 
 SimpleCrypt::SimpleCrypt(quint64 key) :
   m_key(key),
   m_compressionMode(CompressionAlways),
   m_protectionMode(ProtectionHash),
   m_lastError(ErrorNoError) {
-  qsrand(uint(QDateTime::currentMSecsSinceEpoch() & 0xFFFF));
   splitKey();
 }
 
@@ -116,7 +114,7 @@ QByteArray SimpleCrypt::encryptToByteArray(QByteArray plaintext) {
   }
 
   //prepend a random char to the string
-  char randomChar = char(qrand() & 0xFF);
+  char randomChar = char(QRandomGenerator::global()->generate() & 0xFF);
 
   ba = randomChar + integrityProtection + ba;
   int pos(0);
@@ -221,6 +219,7 @@ QByteArray SimpleCrypt::decryptToByteArray(QByteArray cypher) {
     }
 
     quint16 storedChecksum;
+
     {
       QDataStream s(&ba, QIODevice::ReadOnly);
 
diff --git a/src/librssguard/miscellaneous/systemfactory.cpp b/src/librssguard/miscellaneous/systemfactory.cpp
index 635000af7..fc54ecdf1 100644
--- a/src/librssguard/miscellaneous/systemfactory.cpp
+++ b/src/librssguard/miscellaneous/systemfactory.cpp
@@ -59,7 +59,6 @@ SystemFactory::AutoStartStatus SystemFactory::autoStartStatus() const {
     return AutoStartStatus::Disabled;
   }
 #elif defined(Q_OS_LINUX)
-
   // Use proper freedesktop.org way to auto-start the application on Linux.
   // INFO: http://standards.freedesktop.org/autostart-spec/latest/
   const QString desktop_file_location = autostartDesktopFileLocation();
@@ -82,7 +81,6 @@ SystemFactory::AutoStartStatus SystemFactory::autoStartStatus() const {
     return AutoStartStatus::Disabled;
   }
 #else
-
   // Disable auto-start functionality on unsupported platforms.
   return AutoStartStatus::Unavailable;
 #endif
@@ -139,7 +137,6 @@ bool SystemFactory::setAutoStartStatus(AutoStartStatus new_status) {
       return false;
   }
 #elif defined(Q_OS_LINUX)
-
   // Note that we expect here that no other program uses
   // "rssguard.desktop" desktop file.
   const QString destination_file = autostartDesktopFileLocation();
@@ -279,7 +276,8 @@ bool SystemFactory::isVersionEqualOrNewer(const QString& new_version, const QStr
 
 bool SystemFactory::openFolderFile(const QString& file_path) {
 #if defined(Q_OS_WIN)
-  return QProcess::startDetached(QString("explorer.exe /select, \"") + QDir::toNativeSeparators(file_path) + "\"");
+  return QProcess::startDetached(QSL("explorer.exe"),
+                                 { "/select,", QDir::toNativeSeparators(file_path)});
 #else
   const QString folder = QDir::toNativeSeparators(QFileInfo(file_path).absoluteDir().absolutePath());
 
diff --git a/src/librssguard/network-web/adblock/adblockrule.cpp b/src/librssguard/network-web/adblock/adblockrule.cpp
index 5e9e199e5..a2eeed39a 100644
--- a/src/librssguard/network-web/adblock/adblockrule.cpp
+++ b/src/librssguard/network-web/adblock/adblockrule.cpp
@@ -370,7 +370,12 @@ void AdBlockRule::parseFilter() {
   int optionsIndex = parsedLine.indexOf(QL1C('$'));
 
   if (optionsIndex >= 0) {
-    const QStringList options = parsedLine.mid(optionsIndex + 1).split(QL1C(','), QString::SkipEmptyParts);
+    const QStringList options = parsedLine.mid(optionsIndex + 1).split(QL1C(','),
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                                       Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                                       QString::SkipEmptyParts);
+#endif
     int handledOptions = 0;
 
     for (const QString& option : options) {
@@ -497,7 +502,12 @@ void AdBlockRule::parseFilter() {
 }
 
 void AdBlockRule::parseDomains(const QString& domains, const QChar& separator) {
-  QStringList domainsList = domains.split(separator, QString::SkipEmptyParts);
+  QStringList domainsList = domains.split(separator,
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                          Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                          QString::SkipEmptyParts);
+#endif
 
   for (const QString& domain : domainsList) {
     if (domain.isEmpty()) {
@@ -618,15 +628,15 @@ QString AdBlockRule::createRegExpFromFilter(const QString& filter) const {
 }
 
 QList<QStringMatcher> AdBlockRule::createStringMatchers(const QStringList& filters) const {
-  QList<QStringMatcher> matchers;
+  QList<QStringMatcher> mtchrs;
 
-  matchers.reserve(filters.size());
+  mtchrs.reserve(filters.size());
 
   for (const QString& filter : filters) {
-    matchers.append(QStringMatcher(filter, m_caseSensitivity));
+    mtchrs.append(QStringMatcher(filter, m_caseSensitivity));
   }
 
-  return matchers;
+  return mtchrs;
 }
 
 int AdBlockRule::regexMatched(const QString& str, int offset) const {
diff --git a/src/librssguard/network-web/adblock/adblocksearchtree.cpp b/src/librssguard/network-web/adblock/adblocksearchtree.cpp
index 06c5f50fd..232baa796 100644
--- a/src/librssguard/network-web/adblock/adblocksearchtree.cpp
+++ b/src/librssguard/network-web/adblock/adblocksearchtree.cpp
@@ -89,8 +89,7 @@ const AdBlockRule* AdBlockSearchTree::prefixSearch(const QWebEngineUrlRequestInf
     return nullptr;
   }
 
-  QChar c = choppedUrlString.at(0);
-  Node* node = m_root->children.value(c);
+  Node* node = m_root->children.value(choppedUrlString.at(0));
 
   if (node == nullptr) {
     return nullptr;
diff --git a/src/librssguard/network-web/adblock/adblocksubscription.cpp b/src/librssguard/network-web/adblock/adblocksubscription.cpp
index 0cdf0feec..6e4c4602e 100644
--- a/src/librssguard/network-web/adblock/adblocksubscription.cpp
+++ b/src/librssguard/network-web/adblock/adblocksubscription.cpp
@@ -62,7 +62,7 @@
 #include <QTimer>
 #include <utility>
 
-AdBlockSubscription::AdBlockSubscription(QString  title, QObject* parent)
+AdBlockSubscription::AdBlockSubscription(QString title, QObject* parent)
   : QObject(parent), m_reply(nullptr), m_title(std::move(title)), m_updated(false) {}
 
 QString AdBlockSubscription::title() const {
@@ -290,11 +290,11 @@ void AdBlockCustomList::loadSubscription(const QStringList& disabledRules) {
     stream.setCodec("UTF-8");
 
     if (!rules.contains(ddg1 + QL1S("\n"))) {
-      stream << ddg1 << endl;
+      stream << ddg1 << Qt::endl;
     }
 
     if (!rules.contains(QL1S("\n") + ddg2)) {
-      stream << ddg2 << endl;
+      stream << ddg2 << Qt::endl;
     }
   }
 
@@ -313,12 +313,12 @@ void AdBlockCustomList::saveSubscription() {
   QTextStream textStream(&file);
 
   textStream.setCodec("UTF-8");
-  textStream << "Title: " << title() << endl;
-  textStream << "Url: " << url().toString() << endl;
-  textStream << "[Adblock Plus 1.1.1]" << endl;
+  textStream << "Title: " << title() << Qt::endl;
+  textStream << "Url: " << url().toString() << Qt::endl;
+  textStream << "[Adblock Plus 1.1.1]" << Qt::endl;
 
   for (const AdBlockRule* rule : m_rules) {
-    textStream << rule->filter() << endl;
+    textStream << rule->filter() << Qt::endl;
   }
 
   file.close();
diff --git a/src/librssguard/network-web/downloader.cpp b/src/librssguard/network-web/downloader.cpp
index c6650e92c..d7ca09056 100644
--- a/src/librssguard/network-web/downloader.cpp
+++ b/src/librssguard/network-web/downloader.cpp
@@ -181,7 +181,13 @@ QList<HttpResponse> Downloader::decodeMultipartAnswer(QNetworkReply* reply) {
   QString content_type = reply->header(QNetworkRequest::KnownHeaders::ContentTypeHeader).toString();
   QString boundary = content_type.mid(content_type.indexOf(QL1S("boundary=")) + 9);
   QRegularExpression regex(QL1S("--") + boundary + QL1S("(--)?(\\r\\n)?"));
-  QStringList list = QString::fromUtf8(data).split(regex, QString::SplitBehavior::SkipEmptyParts);
+  QStringList list = QString::fromUtf8(data).split(regex,
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                   Qt::SplitBehaviorFlags::SkipEmptyParts);
+#else
+                                                   QString::SkipEmptyParts);
+#endif
+
   QList<HttpResponse> parts;
 
   parts.reserve(list.size());
@@ -197,7 +203,12 @@ QList<HttpResponse> Downloader::decodeMultipartAnswer(QNetworkReply* reply) {
                                             start_of_body - start_of_headers).replace(QRegularExpression(QSL("[\\n\\r]+")),
                                                                                       QSL("\n"));
 
-    for (const QString& header_line : headers.split(QL1C('\n'), QString::SplitBehavior::SkipEmptyParts)) {
+    for (const QString& header_line : headers.split(QL1C('\n'),
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+                                                    Qt::SplitBehaviorFlags::SkipEmptyParts)) {
+#else
+                                                    QString::SkipEmptyParts)) {
+#endif
       int index_colon = header_line.indexOf(QL1C(':'));
 
       if (index_colon > 0) {
diff --git a/src/librssguard/network-web/downloadmanager.cpp b/src/librssguard/network-web/downloadmanager.cpp
index b18dabf59..d5ffe04d0 100644
--- a/src/librssguard/network-web/downloadmanager.cpp
+++ b/src/librssguard/network-web/downloadmanager.cpp
@@ -55,7 +55,13 @@ void DownloadItem::init() {
   m_reply->setParent(this);
 
   connect(m_reply, &QNetworkReply::readyRead, this, &DownloadItem::downloadReadyRead);
+
+#if QT_VERSION >= 0x050F00 // Qt >= 5.15.0
+  connect(m_reply, &QNetworkReply::errorOccurred, this, &DownloadItem::error);
+#else
   connect(m_reply, static_cast<void (QNetworkReply::*)(QNetworkReply::NetworkError)>(&QNetworkReply::error), this, &DownloadItem::error);
+#endif
+
   connect(m_reply, &QNetworkReply::downloadProgress, this, &DownloadItem::downloadProgress);
   connect(m_reply, &QNetworkReply::metaDataChanged, this, &DownloadItem::metaDataChanged);
   connect(m_reply, &QNetworkReply::finished, this, &DownloadItem::finished);
diff --git a/src/librssguard/network-web/webfactory.cpp b/src/librssguard/network-web/webfactory.cpp
index 766c79a13..5dd612b58 100644
--- a/src/librssguard/network-web/webfactory.cpp
+++ b/src/librssguard/network-web/webfactory.cpp
@@ -33,8 +33,7 @@ bool WebFactory::sendMessageViaEmail(const Message& message) {
     const QString browser = qApp->settings()->value(GROUP(Browser), SETTING(Browser::CustomExternalEmailExecutable)).toString();
     const QString arguments = qApp->settings()->value(GROUP(Browser), SETTING(Browser::CustomExternalEmailArguments)).toString();
 
-    return QProcess::startDetached(QString("\"") + browser + QSL("\" ") + arguments.arg(message.m_title,
-                                                                                        stripTags(message.m_contents)));
+    return IOFactory::startProcessDetached(browser, {}, arguments.arg(message.m_title, stripTags(message.m_contents)));
   }
   else {
     // Send it via mailto protocol.
@@ -49,10 +48,11 @@ bool WebFactory::openUrlInExternalBrowser(const QString& url) const {
   if (qApp->settings()->value(GROUP(Browser), SETTING(Browser::CustomExternalBrowserEnabled)).toBool()) {
     const QString browser = qApp->settings()->value(GROUP(Browser), SETTING(Browser::CustomExternalBrowserExecutable)).toString();
     const QString arguments = qApp->settings()->value(GROUP(Browser), SETTING(Browser::CustomExternalBrowserArguments)).toString();
-    const QString call_line = "\"" + browser + "\" \"" + arguments.arg(url) + "\"";
+    auto nice_args = arguments.arg(url);
 
-    qDebug("Running command '%s'.", qPrintable(call_line));
-    const bool result = QProcess::startDetached(call_line);
+    qDebug("Arguments for external browser: '%s'.", qPrintable(nice_args));
+
+    const bool result = IOFactory::startProcessDetached(browser, {}, nice_args);
 
     if (!result) {
       qDebug("External web browser call failed.");
@@ -75,7 +75,6 @@ QString WebFactory::escapeHtml(const QString& html) {
   }
 
   QString output = html;
-
   QMapIterator<QString, QString> i(m_escapes);
 
   while (i.hasNext()) {
@@ -92,7 +91,6 @@ QString WebFactory::deEscapeHtml(const QString& text) {
   }
 
   QString output = text;
-
   QMapIterator<QString, QString> i(m_deEscapes);
 
   while (i.hasNext()) {
@@ -174,6 +172,7 @@ void WebFactory::createMenu(QMenu* menu) {
 
   menu->clear();
   QList<QAction*> actions;
+
   actions << createEngineSettingsAction(tr("Auto-load images"), QWebEngineSettings::AutoLoadImages);
   actions << createEngineSettingsAction(tr("JS enabled"), QWebEngineSettings::JavascriptEnabled);
   actions << createEngineSettingsAction(tr("JS can open popup windows"), QWebEngineSettings::JavascriptCanOpenWindows);
@@ -204,6 +203,7 @@ void WebFactory::webEngineSettingChanged(bool enabled) {
   const QAction* const act = qobject_cast<QAction*>(sender());
 
   QWebEngineSettings::WebAttribute attribute = static_cast<QWebEngineSettings::WebAttribute>(act->data().toInt());
+
   qApp->settings()->setValue(WebEngineAttributes::ID, QString::number(static_cast<int>(attribute)), enabled);
   QWebEngineProfile::defaultProfile()->settings()->setAttribute(attribute, act->isChecked());
 }
diff --git a/src/librssguard/services/abstract/accountcheckmodel.cpp b/src/librssguard/services/abstract/accountcheckmodel.cpp
index 928368976..b686a44c2 100644
--- a/src/librssguard/services/abstract/accountcheckmodel.cpp
+++ b/src/librssguard/services/abstract/accountcheckmodel.cpp
@@ -33,6 +33,7 @@ void AccountCheckModel::setRootItem(RootItem* root_item, bool delete_previous_ro
     m_rootItem->deleteLater();
   }
 
+  m_checkStates.clear();
   m_rootItem = root_item;
 
   if (with_layout_change) {
@@ -172,7 +173,7 @@ QVariant AccountCheckModel::data(const QModelIndex& index, int role) const {
   else if (role == Qt::DecorationRole) {
     auto ic = item->icon();
 
-    return ic.isNull() ? QVariant() : ic;
+    return item->data(0, Qt::ItemDataRole::DecorationRole);
   }
   else if (role == Qt::EditRole) {
     return QVariant::fromValue(item);
@@ -206,6 +207,7 @@ bool AccountCheckModel::setData(const QModelIndex& index, const QVariant& value,
     // Change data for the actual item.
     m_checkStates[item] = static_cast<Qt::CheckState>(value.toInt());
     emit dataChanged(index, index);
+    emit checkStateChanged(item, m_checkStates[item]);
 
     if (m_recursiveChange) {
       return true;
diff --git a/src/librssguard/services/abstract/accountcheckmodel.h b/src/librssguard/services/abstract/accountcheckmodel.h
index c0444461e..f11e027bd 100644
--- a/src/librssguard/services/abstract/accountcheckmodel.h
+++ b/src/librssguard/services/abstract/accountcheckmodel.h
@@ -43,6 +43,9 @@ class AccountCheckModel : public QAbstractItemModel {
     void checkAllItems();
     void uncheckAllItems();
 
+  signals:
+    void checkStateChanged(RootItem* item, Qt::CheckState);
+
   protected:
     RootItem* m_rootItem;
 
diff --git a/src/librssguard/services/inoreader/network/inoreadernetworkfactory.cpp b/src/librssguard/services/inoreader/network/inoreadernetworkfactory.cpp
index c16d88e5c..b98af5297 100644
--- a/src/librssguard/services/inoreader/network/inoreadernetworkfactory.cpp
+++ b/src/librssguard/services/inoreader/network/inoreadernetworkfactory.cpp
@@ -394,9 +394,9 @@ RootItem* InoreaderNetworkFactory::decodeFeedCategoriesData(const QString& categ
     QString title = subscription["title"].toString();
     QString url = subscription["htmlUrl"].toString();
     QString parent_label;
-    QJsonArray categories = subscription["categories"].toArray();
+    QJsonArray assigned_categories = subscription["categories"].toArray();
 
-    for (const QJsonValue& cat : categories) {
+    for (const QJsonValue& cat : assigned_categories) {
       QString potential_id = cat.toObject()["id"].toString();
 
       if (potential_id.contains(QSL("/label/"))) {
diff --git a/src/librssguard/services/owncloud/owncloudfeed.cpp b/src/librssguard/services/owncloud/owncloudfeed.cpp
index 3805a8b7c..7a9ba9ffe 100644
--- a/src/librssguard/services/owncloud/owncloudfeed.cpp
+++ b/src/librssguard/services/owncloud/owncloudfeed.cpp
@@ -22,6 +22,7 @@ bool OwnCloudFeed::canBeEdited() const {
 
 bool OwnCloudFeed::editViaGui() {
   QPointer<FormOwnCloudFeedDetails> form_pointer = new FormOwnCloudFeedDetails(serviceRoot(), qApp->mainFormWidget());
+
   form_pointer.data()->addEditFeed(this, nullptr);
   delete form_pointer.data();
   return false;
@@ -79,6 +80,4 @@ QList<Message> OwnCloudFeed::obtainNewMessages(bool* error_during_obtaining) {
     *error_during_obtaining = false;
     return messages.messages();
   }
-
-  return QList<Message>();
 }