Hacker: Great looking browser of yours! This is gnome, right?
You might want to try Tabbrowser Preferences instead of Tabbrowsesr Extensions. "Extensions" is very powerful; unfortunately, it is also known to cause all kind of problems including memory leaks and javascript incompatibilties. Just a hint, if you are happy with "Extensions", go for it.
Slightly off-topic, but still related to Firefox:
http://windowssecrets.com/041202/#top1 lists severeal Firefox secrets that I am sure even you didn't know about
