Nu är jag inte 100% säker men jag hade samma problem och löste detta.
Problemet var att VLC player lägger en plugin som ska ersätta windows media player i FF.
"Crashes or missing WMP controls while trying to play embedded WMV files
Your browser may crash or, if the video does play, the WMP controls (play/pause/stop) or right-click options may be missing [5]. This can happen when the VLC Media Player is installed and its own browser plug-in takes precedence over the WMP plug-in, causing a conflict. Remove the VLC plug-in file npvlc.dll from the Mozilla Suite or Firefox installation directory plugins folder so that embedded WMV files can play properly. "
taget från
http://kb.mozillazine.org/Windows_Media_Player
Mitt FF krasha inte iofs men wmv filer funkade inte, dock efter borttagning av denna plugin funkar det
mvh/roop