Hey there, you can see how to block and unblock pop up settings here: https://support.mozilla.org/en-US/kb/pop-blocker-settings-exceptions-troubleshooting#w_pop-up-blocker-settings

Also if these are small popups on the bottom right corner of Firefox windows? then these may just be web push notifications from sites you have allowed to send you notifications. Instead of useful information, they may send you junk, spam, fake virus/trojan alerts etc. 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