When Firefox gives me strange issues that I can't figure out or I don't feel like wasting my time with, I usually just
create a new profile. This is essentially starting fresh. A lot of times, especially if you have a lot of extensions, some of your user data can get misconfigured or corrupted.
It would be a good idea to export your bookmarks so you can import them to your new profile. You will also have to reinstall your addons.
Give it a shot. You can always switch back to your old pofile if you need to, as well. Just like how reformatting Windows can fix things, so can this.