I already had Win 7 on my hd and created separate partitions to put OS in each one. Then I did the upgrade Win 10 OS with the tool that was recommended by microsoft. Like I said, once done, it created a folder of Win 7, marked "OldWindows". Then with my Win 7 disc, I did a clean installation of it, thinking I could get some programs and files from that old windows folder. As far as Firefox, it was not working correctly in Win 7. I installed FF for the first time in Win 10. ..even that wasn't working right. Days of tweaking, I finally got Win 10 FF working just fine. So that in mind, I started tweaking Win 7's FF and not having any luck at all. The next time I went to use FF in Win 10, it was all screwed up again and then it hit me, the tweaking I was doing with the Win 7 version, somehow screwed my good win 10 version. So far i am staying away tweaking Win 7 version until I find a way and try to get FF to work in win 7, that it won't affect the Win 10 version. Sorry for the yata de yata.