If these are small popups on the bottom right corner of Firefox windows then these may just be web push notifications from sites you have allowed to send you notifications. Instead of useful information, some may send you junk, spam, fake virus/trojan alerts etc. You can revoke the sites from sending you notifications as shown in second link below.

https://support.mozilla.org/en-US/kb/push-notifications-firefox https://support.mozilla.org/en-US/kb/push-notifications-firefox#w_how-do-i-revoke-web-push-permissions-for-a-specific-site

I solved it eventually by doing a " shift restart " . Cost me about 2 hours to track down a solution . Then have had to reenter a number of ` log-ins " . But did save my windows , some of which I deleted as possibly being related to the problem .

Hi Bob

Glad to hear the problem has been resolved.