Comment 1 for bug 369880

Occurs for me too, both under Jaunty i386 Firefox 3.0 and Karmic beta amd64 Firefox 3.5.

Doesn't happen under Windows with Firefox 3.0 or 3.5, or under Slax with Firefox 3.5 and KDE 3.5: maybe it's a GNOME problem. I'm running a UK keyboard layout with no IME (on Karmic ibus is installed, but not running) and no xorg.conf.

See http://unixpapa.com/js/testkey.html for a test case. When a non-shifting key is held, Firefox produces:

    keydown
    keypress
    keyup
    keydown
    keypress
    keyup

Most other browsers produce:

    keydown
    keypress
    keydown
    keypress
    keyup

(Some produce:

    keydown
    keypress
    keypress
    onkeyup

but this is a well-known variation which is easily coded around. The current Firefox behaviour, on the other hand, cannot be worked around as the key event stream is indistinguishable from a user hammering repeatedly on the key. This breaks in-browser games quite badly.

Judging by this post:

    http://actionscript3.blogs2k.com/2009/08/19/ActionScript%203%20-%20keyboard-event-capturing-in-linux%20-AS3

The same problem may be visible from Flash.