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 Are these small popups in the bottom right corner of Firefox windows?. If so then these are likely just 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. You can revoke these sites from sending you notifications. Also Firefox for Windows, macOS, Linux is a web browser and not a anitivirus client.