It was working fine. But, no longer. I have chosen custom URL (https ://www google com /advanced_search). It doesn't go there upon opening new tab.
It may have been updating firefox to 136.0.4. (spaces added to URL - review does not allow otherwise)

EDIT: Okay, now I got it work. I had to uninstall it and re-install. Something Firefox did somewhere broke it, but I can't say what. I certainly never touched it.