Bug-org 672193 has been fixed. So, now, Thunderbird can be improved more familiar with multimedia keyboards on Windows. And if the handler wants to prevent the default behavior of keyboard utility, it should call preventDefault() rather than stopPropagation(). Current code doesn't call preventDefault() that may cause same action happened twice. Here is the current event handler: http://mxr.mozilla.org/comm-central/source/mozilla/browser/components/places/content/places.js#98 And I think that similar handler should also be implemented on composing window and/or something.