Bug 1700706 - Clear active and capturing content before opening native menus. r=tnikkel

This is copied from the nsMenuPopupFrame::ShowPopup just a few lines below.
The native menu consumes mouseup events so we need to clear :active and capturing content just before opening the menu.

Differential Revision: https://phabricator.services.mozilla.com/D109672

layout/xul/nsMenuPopupFrame.cpp

@@ -958,6 +958,17 @@ void nsMenuPopupFrame::InitializePopupAtRect(nsIContent* aTriggerContent,
 
 void nsMenuPopupFrame::ShowNativeMenu() {
   MOZ_RELEASE_ASSERT(mNativeMenu);
+
+  // While the native menu is open, it consumes mouseup events.
+  // Clear any :active state and mouse capture now so that we don't get stuck in
+  // that state.
+  EventStateManager* activeESM = static_cast<EventStateManager*>(
+      EventStateManager::GetActiveEventStateManager());
+  if (activeESM) {
+    EventStateManager::ClearGlobalActiveContent(activeESM);
+  }
+  PresShell::ReleaseCapturingContent();
+
   bool succeeded = mNativeMenu->ShowAsContextMenu(
       DesktopPoint::FromUnknownPoint(mScreenRect.TopLeft()));
   if (!succeeded) {