Well I just want to let you know, they now get along. ^_^
Turns out the problem was our SoundCloud powered media player.
Apparently SoundCloud provides the player in both an object and embed tag, with allowscriptaccess on and Firefox doesn't like the fact that the embed tag it's in that hover box I made for it with allowscriptaccess on.
Yes, I know. Doesn't make sense/confusing.
I'm just going to report this to Mozilla and call it a day.