[gpm]

Mozilla didn't really "break your browser remotely", it's more like there was a time bomb included that just went off.

If you try hard enough you can probably fix your browser, unpack the .xpi (it's just a zip), look at the source in experiments/skeleton, and try to figure out how to run something similar in the browser console.

But I really can't recommend doing this, I appreciate it's painful, but what you're running right now is massively insecure, there are published exploits. You're just asking for viruses by interacting with the internet using something that old.