I just had a friend tip me off that he sees the full menu in IE, so this seems like a Firefox incompatibility, since his Firefox doesn’t show it either.
Edit: Huzzah! By going into my Firefox settings, I’ve been able to get the TinyMCE menu to re-appear in OS X:
Firefox > Options > Content > Enable Javascript > Advanced > Make sure all these options are checked.
Credit goes to dracolich for this fix. Hope this works for everyone!