Are these small popups on the bottom right corner? if so then these are not from Firefox web browser but are web push notifications from sites you have allowed to send you notifications. Unfortunately some can be junk, spam, fake virus alerts and such instead of useful information. You can revoke those 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