The only reason why Brendan Eich's contribution should be an issue is because he's now the CEO of Mozilla and people are afraid that his personal beliefs on the matter will affect Mozilla. But that worry is only justified when talking about the CEO (or I suppose the Director of Human Resources, or whatever the equivalent at Mozilla is).
And even that I think might be an overreaction. From everything Brendan Eich has said publicly, it appears that he wants to keep his personal beliefs private, and that he's committed to everything Mozilla stands for in his public role as CEO. So I'm not worried that he's going to turn Mozilla into a bad work environment for gay employees. My only real worry is that he will not be proactive about improving conditions or about supporting relevant community initiatives, but the same could be said of a CEO that has no opinion whatsoever on gay marriage.
In any case, OKCupid has taken public actions (e.g. their message to Firefox users) that indicate that, as a company, they come down in favor of gay marriage. The individual beliefs and actions of their rank & file employees should not matter in the slightest.