Thank you, the workaround with widget.gtk.ignore-bogus-leave-notify works. And yes the temporary fix was kind of weird, as it used to work if I launched firefox directly, but not when it was started by clicking some link in other applications.

I see. Thank you for the explanation as well!

This worked, thank you. Would you mind telling what difference between using urlbar-background over the other one?

Thank you, it worked.