Are these as small popups on the bottom right corner of Firefox windows? if so then these may just be web push notifications from site(s) you have allowed to send you notifications. You can revoke these 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