Mozilla has the right to fire whomever they like for whatever reason they please, though I find the marriage equality movement (which I of course support) distasteful at times (see Chick-Fil-A) and this is one of the reasons why.
Wait, what? Chick-fil-A had the best business day in their entire history when all the fatass rednecks in the South waited over an hour for some greasy fast food just to stick it to Obama and all those libruls (as if they cared). To this day, right-wing Christians really think they're doing something by packing out Chick-fil-A. If anyone is embarrassing or "distasteful," it's all of those idiots.
Making anti-gay marriage statements was a brilliant business ploy for Chick-fil-A, gaining them many more customers than they lost (hell, I still eat there once a month or so). If I owned a restaurant, I'd probably make some statements like that too just to get business.
All it took was the pearl clutching to get all of those people into their stores. The negative reaction lead to a much greater positive reaction.