The only thing I could suggest is an uninstall/reinstall, and by uninstall I mean using Firefox's uninstaller first, followed by something like Revo Uninstaller just to make sure that every bit of it has been purged before reinstalling.
It would also be helpful if you would publish a Speccy system snapshot and provide the web address for it in your message. Here are downloadable step-by-step instructions for doing this:
- Using Speccy, PDF Format
- Using Speccy, MS-Word Format
Also, are you certain that all of your device drivers, and particularly display drivers, are on the latest versions for the hardware and OS you're running? Certain really flaky problems are not, directly anyway, the fault of a given program but in how it's interacting with devices. Developers expect certain things to be happening in a certain way, and if they're not, havoc can ensue.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Presenting the willfully ignorant with facts is the very definition of casting pearls before swine.
~ Brian Vogel