I have a problem with playing videos with seamonkey 1.0.3 and mplayerplug-in. www.realmadrid.com videos (on the center of the screen any video where isn't a lock sign). If I try to play it, with selecting the correct link, and on the popup window pressing play button, only a grey box will appear without mplayer controls and it seems like mplayerplug-in doesn't start. Interesting is that it works find with seamonkey 1.0.2 and mplayerplug-in.
Here is an example: