I have the exact same problem, Firefox says it needs to restart to install the addons I downloaded, but when I restart it just says the exact same thing.

Hello.

This happens, to my knowledge, when Firefox's extension files are corrupt. I know there is a fix for this somewhere, but I don't really know what it is. Try canceling the install process and trying again, instead of endless pressing "restart now".

But don't give up, there's a fix somewhere. Hopefully someone here will know what it is.

I have tried removing the extensions files that doesn't fix it. I have searched through the forums and I have tried everything that has been suggested so far.

the same 2 java updates and a noscript update fail to install FF 3.6.6 Windoze XP 01

Getting tired of seeing it not happening despite endless restarts, now I just hit skip....

Hey again, I did a complete uninstall and reinstall of Firefox and it fixed the problem for me.