The idea is to give users a chance to open a bona fide pop-up even though pop-ups are "blocked" and are less of an annoyance (since they won't pop up fully but are collected like in your screenshot).

If all pop-ups were silently 100% suppressed, some sites might essentially break.

Hello Firefoxor,

Would you try this please :

When you're on that site, click on the 'i' in a circle, next to the padlock at the left side of the address bar.

Then click on the little black arrow on the dropdown (next to 'Connection') and then on "More Information", which will take you to "Page Info".

Click on the 'Permissions" tab and scroll down to "Open Pop-up Windows". Uncheck "Use Default" and check "Allow".

Then close and restart Firefox.

Also : In Options => Privacy & Security => under "Permissions": add the site to "Exceptions".

'Hope that helps .....