If you get a pop-up message asking to update Firefox or plugins or scanning for malware then such a message is likely a scam and you should NEVER respond to such an alert to avoid getting infected with malware.

• only update Firefox via "Help -> About" or by downloading and installing Firefox from the Mozilla and never via a pop-up or link on a web page.

See also:

• https://support.mozilla.org/en-US/kb/i-found-fake-firefox-update
• https://support.mozilla.org/en-US/kb/avoid-and-report-mozilla-tech-support-scams

Are these as small popups on bottom right corner of Firefox windows?. If so 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 these sites from sending you notifications.

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