Firefox seems to be more picky about html comment tags than IE. Actually I should say the opposite is true: IE lets you get away with being more sloppy with your html comment tags than FF. Technically, there should be no double-dash code (--) within a commented out sequence. For max safety each line should be commented out separately. You can get away with 'bending' the rules in IE, but not FF. I often forget to check the code in FF, so this serves as a good reminder.
I just erased the "commented out" sequence and fixed the problem.