Here's a couple of other differences that might be worth reflecting on:
1. What support Eich provided for proposed law vs actions he's likely to support as CEO -- in other words, what you can actually tell about Eich by the fact that he provided financial support for the law, and what you might know about him by considering a larger totality of his actions.
If you want a parallel, consider what Janis Ian has said about Orson Scott Card:
2. Now vs then. In 2008, the then president of the united states supported prop 8. The current president of the US was on record as not sure about it (and against gay marriage). If we're talking about the height of the profile of a position -- and you seem to be in making a distinction between an employee and CEO -- then I'd say leadership of Mozilla is pretty pale by comparison.
3. While Mozilla is arguably a "values" organization (presumably an important distinction), it's working in a sphere that's pretty orthogonal from identity-minority rights. If you'd argue that doesn't matter, I suppose that's one approach, but if so, I presume that you'd also decide that GLAAD should also be generally boycotted because of their 2011 support of the T-Mobile/AT&T merger and opposition to Net Neutrality principles.
I think we do not share the same opinion about the significance of those differences. But that is ok. I promise not to boycott your company because you have a different belief than me.
2. There is a difference between being employed by a company and being its CEO.
3. These differences are significant.