I'm not suggesting that Francine and her family are poor by any means, but I do wonder if they were meant to be depicted as not quite as well off as others in Elwood City... it seems to be rather subtly suggested at times: their apartment is typical of lower-income housing (I've lived in apartments like theirs before, they're usually really low rent, in seedy neighborhoods, not to say Elwood City has any seedy neighborhoods), one episode deals with Francine not wanting to be seen riding her dad's old bicycle since they can't afford to get her a new one, it's a little more in the open when Muffy moves in with them temporarily (though, it's probably more artistic license to contrast Muffy being accustomed to her wealthy lifestyle, and having to adjust to the Frensky's not as rich lifestyle).