I had almost 80 extensions before Firefox 2 came out (when I decided to trim out some of the less-useful ones, not to mention the ones for features that are now built in) without trying to add any useless ones.

I’ve trimmed it down to just under 50 now and I find Menu Editor particularly helpful for managing all the redundant menu entries caused by them (such as items appearing on the toolbar, Tools menu AND the context menu).