It not as good as the one I had before I reinstalled my OS and made a backup of wrong FF folder – it's damn slow and lets all popups open, but closes them a second later, so it does its job as intended. For me good enough, if dev will manage to actually block popups then it will be delightful.
I'm not sure though if „block all tabs” settings should prohibit user from opening anything, even if it's clearly at his will (like opening bookmark or new tab at all). I guess all really means all here, heh.