Unfortunately, there is a conflict on some computers (don't ask me why on some computers, because I don't know; it applies to my Vista, as well), between ThreadFire, and installing FF add-ons. I posted at ThreadFire forum, but they seem to be slow to solve it.
What you have to do is, BEFORE you install any FF add-on, right click on ThreadFire icon, and click Suspend. The add-on will install with no problem.
Now, there is a very same conflict regarding clicking on add-on's Options, causing FF to freeze.
Apparently, that particular add-on wasn't correctly installed, because of the above conflict.
Suspend ThreatFire, and reinstall add-on (you don't have to uninstall; installing over the top works fine).
Restart FF, and Options shouldn't freeze FF anymore.
Note: Despite the above inconvenience, I keep ThreatFire, because I think, it's a very good program.