Most likely it’s an ad from one of your open Firefox tabs. Try exiting all your web browsers and see if that fixes it.

Very weird site. It implies this is some kind of Swedish version of chatgpt, but it says that it provides the English version. Also, it’s completely hidden who is running this and what company. I would guess they try to steal user information.

There is no guarantee that the released app is exactly the same as the source code when getting it on Google Play. You’d have to decompile or compile from source and try to compare.

Using F-Droid is good alternative.