Comment 6 for bug 1165649

I just checked with xev, and the hardware volume keys do not result in any key event delivered to Firefox. However, hitting the volume keys causes a window to pop up showing the volume, and the current window receives a couple of FocusOut events followed by a FocusIn event. Firefox automatically un-fullscreens when it loses focus.

The same behavior occurs for hardware brightness keys, or anything else that causes a window to pop up. I checked with GNOME2, and KiBi on #xorg-devel confirmed that the same behavior occurs with GNOME3. I suspect that LXDE, Unity, and other desktop environments have the same behavior.

I'd actually suggest that a more sensible fix would involve changing the volume display window and similar on-screen display popups to not take focus, since they don't need to accept input. I don't see any way that Firefox can distinguish between losing focus to the volume display window and losing focus due to Alt-Tab or some other reason that should cause un-fullscreening.

I've marked this Firefox bug as INVALID, because I don't think Firefox can fix it. I've filed https://bugzilla.gnome.org/show_bug.cgi?id=667110 on gnome-settings-daemon to get this fixed in GNOME 3. Users of other desktop environments should file similar bugs.