Does this happen in safe mode? It not, try to troubleshoot like this. Will that work?

I did open firefox in safe mode (after having to restart my computer to get firefox to open again), and now it seems to work.

What do I do from here? I have add-ons for a reason. How do I know which add-on is causing the issue?

Thank you for responding, by the way.

Just disable all add-ons via the safe mode dialog. Then re-enable them one by one, check for the issue after enabling each. After you enable a troublesome add-on, the issue will start happening... meaning you find the culprit!

The solution would be to stop using it and find alternative ways to do the same function. You can also notify the troublesome add-on author of the issue for it to be fixed in a next release of the add-on.