Hello Chas:
As I recall, you use Mozilla for a browser. I too would use it but, I aspire to becoming a competent comp. troubleshooter and view any problems I have with my system as a learning experience.
Last month I picked up a newer version of an old virus, a dialer. It proved to be really tough to get rid of. The final solution lay in editing the registry and increasing my IE security setting to max.
I have tried using a third party firewall, ZA Pro, but due to my slow web connection, I am unable to download large software programs that function 100%. The only exception being updates from MS. Seemingly, they allow for this sort of thing and as installation is proceeding, you have to remain online. As installation proceeds, it will stop here and there and data tranfer from MS will start and seemingly repair the data as installation progresses.
Regards
Greg