The goal is to make firefox work on windows 10, and it eventually will. Right now, there are still some issues with firefox and windows 10, but most of them should be fixed by the time windows 10 is released.

Most important to me - will I retain all my bookmarks AND bookmark tags? I have years worth of important info stored there.

I have done all the right things and made it my default and it still pops up unsafe site. However it works on my husbands and we both downloaded windows 10 at the same time !

A month after newmozguy's post, I just upgraded from Win 7, 64-bit to Win 10, 64-bit. I had the latest version of Firefox (40.0.2) running on Windows 7, and it still works as well as always on Windows 10. All my bookmarks, add-ons, plug-ins, themes, and preferences remained intact. Mozilla made good on its statement that they were going to try to have Firefox ready by the time Windows 10 was released. Thank you, Mozilla team, for your excellent work.