The position is that FF is working fine again.
At a loss to understand why, but very happy to have it working
as Firefox is my favourite.
Virus scans produced nothing, thankfully.
Unless anyone wishes to make a further comment I will close the thread.
I very much appreciate all the suggestions, and the time taken to help me
out with this problem.
Daniweb is a great site, and folks are always extremely helpful and unstinting
with their time.