I had a fully updated Win8.1 system that I installed the new .iso on top. (Foolishly I thought I was building a dual boot system, but I screwed it up) Now Win 10 seems to be pretty well behaved except FF (and also IE) crashes on opening. My Thunderbird email works just fine, and I managed to get to this forum using Tango Browser from the Store. When I try to run any of the troubleshooters, they start to open and immediately exit. I have a very nice Lenovo Ultrabook with an i7 CPU and SSD and 8GB RAM. Any ideas why this selective crashing? One other tidbit,: I had Virtual Box version that was working, but slowly. It also now crashes on opening.