You got it! After the fix ran, everything was fine with the Internet Explorer. No pop up.
Then I started Firefox - and it began again. In both browsers…
Closing down Firefox, stopped it.

I suppose, this is not solving the Problem. But I am so happy for the moment, just to get rid of this annoying message and to continue a bit of my work… Thank you so much!

But: what will be the be the next step? Could you help me further to bring anything on the “right way”?
No more Firefox for me? (haven’t used anything else for years). Any further Reparation scans?