Yesterday evening I've tryed to download some plugins for my new release of Firefox (1.0SR), in particular the Macromedia Flash Plugin and the updated skins available (updates from my previous Firefox release).
I've never had problems with the automatic update feature of Firefox but yesterday was impossible for me to download any updates. 
Someone has found the same problem? Maybe a little incompatibility with XP SP2 (that I've installed on my machine)? Curious...