I know that I've never had problems logging in with Firefox, but I know others who have. I haven't gotten an update to 250MB, but I know others who have. Apparently it's based on the region you're in, and I haven't gotten the storage update, even though I put in my info as being in USA, so it must do it by IP as well.
Paranoia says they'd be doing that just to cause added confusion with using "other browsers" to make support for any non-MS software very difficult. But I don't know if they'd even go through the trouble (though they did with Opera, it just wasn't as random). Who knows though, anything's possible. We don't see the server side scripts.