Hi Dieter, Firefox communicates directly with websites and doesn't run through Mozilla, so I suggest focusing on whether any bad add-on or other malware might have gotten onto your system.

Here's my suggested procedure:

(1) Open the Windows Control Panel, Apps & Features, Add or Remove Programs.

After the list loads, click the control next to Sort by and change from Name to Install date to group the infections, I mean, additions, by date. This can help in smoking out undisclosed bundle items that snuck in with some software you agreed to install. Be suspicious of everything you do not recognize/remember, as malware often uses important or innocent sounding names to discourage you from removing it.

Take out as much trash as possible here. If you're not sure, feel free to post program names or a screenshot of the list.

(2) Open Firefox's Add-ons page using either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• Command+Shift+a (Windows: Ctrl+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions.

Then cast a critical eye over the list on the right side. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove).

Any improvement?

(3) You can search for remaining issues with the scanning/cleaning tools listed in this support article: Troubleshoot Firefox issues caused by malware. These on-demand scanners are free and take considerable time to run. If they finish quickly and especially if they require payment, you may have a serious infection. I suggest the specialized forums listed in the article in that case.

Hopefully that will flush anything on your system and in your Firefox that could be causing this problem.

Thanks for the quick reply.

I have gone through all the steps above (right now still checking for invisible malware with the cleaning tools)

So far no luck. All the programs on my PC are installed by me and my sis has no rights for any installations via the PC unless it is from browsers like Steam (which I cleared as trusted).

I will add two pictures I took this morning. It seems it is from some "club" thing.

I am checking my entire system for anything related to that.

DieterMorgan said

It seems it is from some "club" thing.

Hello DieterMorgan,

This is that "club thing":

https://malwaretips.com/blogs/remove-maranhesduve-club/

Many thx :3

This malware snuck onto an update of one of my Firefox addons.

It was safely removed by the programs you offered :3

Now I added it manually into my watch lists, to ensure it won't leech back onto my system :3

Many thanks for the quick responses. :D