Have not been able to get Flash Player to work since installing Windows 10...My PC is 64 bit, using Mozilla Firefox. None of the troubleshooting tips have worked. Please, any other ideas?

Flash Player works with 64-bit Firefox on Windows 10.   I'm going to need a little bit more to go on.

I'd start by downloading Flash Player using Firefox here, then running the installer:

http://get.adobe.com/flashplayer/

Do you have any ad-blocking / anti-tracking / anti-javascript plug-ins running that might interfere with pages trying to load Flash?