Certain content-blocking extensions like AdBlock for Firefox or uBlock Origin can block popups like that in some cases.

However, they aren't blocking in all cases, since a lot of content blockers don't treat them as an advertisement. Plus, using content blockers can cause additional popups telling you to disable your ad blocker.

Thank you , I've tried both of those. I wonder if something the " about: config " would do anything?

No. Firefox loads what the website tells it to load, which in this case is a popup box. But since it's not technically a "popup" because it's in the same tab as the website, it's not something that the built-in Firefox popup blocker will detect.

I don't normally listen to anyone who puts pineapple on pizza but Thank you Wesley ;) Perhaps Mozilla will fix this some day

No problem! :)