Several users have reported problems with Mozilla Firefox in Windows 10. Firefox's unanswered error is one of the most common errors associated with this browser. Users report that this is the first time this has happened since Windows Update.
When Mozilla Firefox stops working, it stops responding to your clicks, keyboard clicks, as if it's doing nothing. Also, the Firefox title bar does not respond, the mouse cursor becomes a spinning wheel on the Firefox window.
While there are many reasons for this, some common culprits seem to be responsible for the web browser problem.

malicious attacker files
Several free software converters work in Firefox at the same time.
Firefox cannot create files in the profile folder simply because they are read-only.
Offensive plugins.
https://sites.google.com/view/firefoxx-not-working/