firefox popups warning of virus cannot remove

https://support.mozilla.org/en-US/kb/push-notifications-firefox#w_how-do-i-revoke-web-push-permissions-for-a-specific-site Are these as small popups on the bottom right corner of Firefox window? 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.