xev:

KeyRelease event, serial 37, synthetic NO, window 0x5600001,
    root 0x4a8, subw 0x0, time 86926485, (515,646), root:(2473,721),
    state 0x0, keycode 90 (keysym 0x1008ff4b, XF86LaunchB), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

xbindkeys -s:

"/usr/bin/firefox-trunk bbc.co.uk"
    XF86LaunchB