XFCE Dell Vostro 3560 function keys / buttons

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I have the following issues with some special keys and buttons on my Dell Vostro 3560:

• Function+F1 (display output toggle): never tried (xev reports some sort of Super_L + Return combination)
• Function+F2 (wireless switch): working (xev reports XF86WLAN)
• Function+F3 (touchpad toggle): not working (xev reports XF86TouchpadToggle)
• Function+F4 (brightness down): working (xev reports no specific keycode)
• Function+F5 (brightness up): not working (xev reports no specific keycode)
• Function+F8/F9/F10 (previous/play-mute/next): working (xev reports XF86AudioPrev, XF86AudioPlay and XF86AudioNext)
• Function+F11/F12 (volume down/up): working (xev: no specific keycode)
• Mute: Does mute the sound but does not toggle back to unmuted. Notification popup is correct but somehow pulse audio mixer remains muted.
• I have three buttons (first one advertised as Quick Recovery button) in the upper right section above my keyboard. First button seems mapped to Super_L + x (how? why?) the two others don't even generate an X event. It would be nice to reassign them to useful functions (i.e. launch a browser, open a terminal, etc...).

How can I fix those problems?