So you're running it in safe mode? If so, stop, that's just a quick way to check whether it's likely to be addons.
Or are you saying you can't get to tools>addons in normal mode?
If you can't then it sounds dodgy, yeah. Easiest to just make a new profile (especially if you have syncing on, though be careful what it syncs). Or use Chrome.
If you can then just disable all the plugins and extensions and enable them one by one.