Are these 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. Unfortunately some sites may send you junk, spam, fake virus alerts including fake alerts from McAfee instead of useful information. You can revoke these sites. 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