'm no guru, but have some guesses maybe worth trying:
(a) Is there a firefox add-in for OE still installed?
(b) Has IE been reset as the default Browser?  It wont hurt
    to redo it manually.
(c)  Is the FILE ASSOCIALTIONwith htm files reset to IE?
    [ find any htm file on C:, right click, slsect "choose program", pick IE form list,
    and finally check the box called "always use this program..."