Shift+F10 is also well-known shortcut key on Linux. So, it should behave same as pressing ContextMenu key. So, for allowing web page to prevent its default, nsWindow for GTK needs to consume Shift key state at dispatching eContextMenu key.
Additionally, we should allow to open context menu with Shift+ContextMenu because only ContextMenu key press can be prevented its default by web page. Therefore, we should allow users to open context menu even with keyboard even if web content doesn't want it.
Note that Ctrl+Shift+F10 or Alt+Shift+F10 should behave same as Shift+ContextMenu key, but we should discuss later.
MozReview-Commit-ID: 1mPGKMTsrkv
Using direction-changed signal, we detect keyboard change for bidi.
When system uses fcitx's IM and ibus's arabic keyboard layout, this signal might fire often when switching layout and gdk_keymap_get_direction might return invalid bidi information. But I think that this is rare issue. Most users don't use Firefox Arabic version (it means that bidi.browser.ui = true) with ibus Arabic layout and fcitx CJK IM. Since there is no GTK3 API to get current IM module, I cannot find workaround for this.
MozReview-Commit-ID: DL8uUXJFWYz
