A number of visitors, including myself, have been experiencing random video playback problems with the new Firefox (3.0.3) [and Opera it seems] and the Flash plugin on the Windows platform. Googling the issue has thrown up a whole load of different solutions, none of which have worked for me.
Very frustrating.
Strangely, checking video clips that were posted on here via YouTube before Flash plugin version 9 play fine.
So maybe it is a three way issue with how YouTube are streaming to the Flash plugin via Firefox…
Doing a few tests, the only solution I found was to uninstall Flash plugin version 9 and install Flash plug in version 8. This works for both Firefox and Opera browsers.
You can download the Flash Uninstaller from Adobe here.
Get the Flash 8 plugin from Adobe here. (unfortunately you have to download the 22mb fp8_archive, unzip it, look in the folder called ‘r42‘ then launch the file ‘flashplayer8r42_win.exe‘)
Alternatively, Google flashplayer8r42_win.exe and you will find the stand alone installer.