I tried to use Firefox at Movable Style with the really neat Modern Lines style sheet last night and it worked great – I really like the clean look for it (but shouldn’t it be called Movable Styles?). However for best effect the Style Selector plugin needs to be installed as you can then switch between styles from the icon in the bottom right of the statusbar (as well as from the drop down list on the web page). The annoying thing is that the styleselector extension has gone missing from the Firefox list of plugins. It does still work though as I’m using it right now.
Incidentally I tried using the EditCSS plugin to see what this page would look like with the Modern_lines style and the date text disappears which is annoying and it was too late last night to work out why (and too early right now to try again)