Internet explorer and mybb
/end unsolicited butting in
You didn't mention IE 6. (I understand why - just thinking about IE 6 gives me nightmares.) The life of all HTML coders everywhere would be SO much easier if IE could just be nuked from orbit.
Microsoft have deprecated it. They chucked it out in the trash and I (and many other developers) are GLEEFULLY nailing the lid on the trashcan.