Here’s a easy way to keep your firefox extensions backed up. You know all those cool ones you’ve found or discovered by accident and you’d probably have trouble getting them all again after you reinstall Windows?
It’s called FEBE.
FEBE ( Firefox Environment Backup Extension) allows you to quickly and easily backup your Firefox extensions. In fact, it goes beyond just backing up — It will actually rebuild your extensions individually into installable .xpi files. Now you can easily synchronize your office and home browsers. And you can schedule your backups to run automatically too. Very handy.
Have read of it here
As far as what extensions you should be using with firefox, there are a lot of threads out there on the net so I won’t bother flogging my opinion on it – each one of us had their own personal needs, but as with most people, when I reinstall I will want all the extensions back again without wasting time looking, downloading and installing them again.