When I watch a clip in a tab with firefox and I close this tab while the movie is playing, firefox freezes.
It will not freeze, if I kill the mplayer by pressing 'q'.
try mplayerplug-in CVS
try a new version of mplayer
try current firefox
What version of glibc are you running?
With mplayerplug-in 2.80 it works.
What version where you using?
I was using 2.66. Which is stable on gentoo. 2.80 is the testing version.