Are these small popups on the bottom right corner of Firefox windows? If so then thee 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 or fake virus/trojan alerts in their attempts to try and infect you. This does not mean you are infected. You can revoke 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