Unless Mozilla has entered into business of organizing gay weddings while I wasn't looking - no, it's not reasonable at all. No more than gun owner should be concerned if his CEO donated to a known anti-gun politician, or a medical marijuana user should be concerned if his business partner donated to a politician that opposes drug legalization. There was nothing in Eich's actions that would concern his employees and business partners in their capacity as employees and business partners. As far as it is known, he didn't say he would fire gay people (and he didn't do that either), he didn't say he would deny them benefits if affording such benefits were recognized by the law, he didn't refuse to enter any deals because opposing side was represented by gay person - in short, he did absolutely nothing of the sort that may raise such reasonable suspicion. The only base for that is "he's for prop 8, so he must be despicable person, so he's evil, so we have reasonable suspicion he would hate us because that's what evil people do". It's not an argument, it's a series of stretches, one worse than the other.