When a notification comes up on one of the pages open, or, videos in Twitter/Facebook feed automatically start playing - Firefox pauses Windows Media Player. Music automatically resumes after I force stop videos or a second after notification. Couldn't find option to prevent Firefox from doing that, and don't want to disable automatic playback of videos, since it won't stop notifications or other sounds from pausing WMP. No such problems with other media players (MPC for example), or with other browsers and WMP.