One thing that might be worth a try is to uninstall Firefox again and then get CCleaner to do a cleanup and then a registry clean. I usually do that duo two or three times as one seems to free stuff up for the other to find next time round. I'm just wondering if the rollback didn't actually delete the Firefox files and the FF installer found them and didn't bother writing over them thoroughly?
If that doesn't work, and I don't often agree with people that suggest doing a fresh Windows installation, but I think it may just be the easiest thing to do, especially since you've taken it back to near 'as new'. Get the SSD and it'll be done in no time. I can send you a Win7 disc if you haven't got one.
CCleaner (get the free one) here:-
https://www.piriform.com/ccleaner/download