I am still waiting for my ISP to let me know what the password is for my Tbird account (I don't see why this should be hard) - I will hassle them again after Easter. In the meantime I have modified it so all new messages which arrive there get automatically forwarded to my Gmail account and then get deleted from it. This works - today the standard "There is a new post in a NT thread that you have contributed to." advisories appeared in my Gmail account.

The other thing that I have learned through trial and error is that System Restore is not the same in Win10 as it is in Win7. In Win7 it just removes new programs and program updates but does not touch new datafiles but in Win10 it removes new datafiles as well. Grrr...

Everything was backed up on my external HD so I spent a tedious few hours putting everything back.