Hi Jim, some users have been testing Firefox on the Windows 10 preview. The problems I've seen reported here on the forums are the usual kinds of things, except that for a while it was impossible to print. Hopefully that has been resolved by now. If you want to see past discussion, this query shows the 80 threads that mention "windows 10": https://support.mozilla.org/search/advanced?q=%22windows+10%22&product=firefox&sortby=0&a=1&w=2