Microsoft is always trying to break FireFox in Win10, just back up your Profile Folder, uninstall FireFox and reinstall it. Every time Update Tuesday rolls around, Win10 updates erase some of the Registry entries that allow FireFox to run properly.
I used to Beta test OSes for MS, they started doing this to FireFox back during Vista development. All Edge is is IE5 stripped to its' core with a new set of APIs, it isn't even a totally new browser like MS claims it is. Don't believe the Marketing wank.