Alright.. I resisted a couple days before getting extentions.. but I finally went and checked out what they had to offer.. already I'm amazed and love what I've downloaded.. never knew what I was missing until I got more, but now I don't know if I could ever go back
Anyways, I ran into a problem that I image a few people may have (those on *nix, at least). I su'd to root and installed all the extensions I wanted.. as I was guessing some would need root no matter what (like Optimoz Mouse Gestures used to for Firebird). I was pleasantly surprised that most extensions had the option to install locally.. anyways.. some that I installed system-wide wouldn't load for me (as a normal user). As a result, it was locking up every session of Firefox. What you need to do is allow rx permissions to the jar files in your Firefox chrome directory.
On Gentoo (and probably a lot of other distros), the Firefox chrome directory is:
/usr/lib/MozillaFirefox/chrome. Then you need to chmod -R 755 *.
For example:
latch@afx latch $ su
Password: [put in your root password]
root@afx latch # cd /usr/lib/MozillaFirefox/chrome
root@afx chrome # chmod -R 755 *
root@afx chrome # exit
exit
latch@afx latch $
Firefox should then load successfully for you