Are you sure it is optional? [1]
In any case Mozilla does offer them. So what exactly is the problem? What would change with or without gay marriage recognized by California? If anything, this shows that while Eich may be opposed to gay marriage, he is not at all opposed to equal benefits (unless of course you could point to instance where he tried to remove that policy).
True, but a) Mozilla had benefits equality all along anyway, and b) California moved to equalize benefits way before prop 8 was overturned, see my link above or look it up - for almost all matters except calling it "marriage", domestic partnerships in California have the same meaning as "marriage" for about a decade now. The whole hoopla seems to be exclusively about calling it "marriage", not about any benefits or any economic or legal matters.
If that were true then would you consider it right to oust Mr Eich because the company in which he only just became CEO abides by the law? Wouldn't it be more mature, and democratic, to request that the company adjusted to allow people equal benefits regardless of their beliefs about sexuality and then take action if they refuse.