1) To have a political position on this issue. 2) To enforce that political position on all of its employees.
#1 is somewhat reasonable (that is, it's a bit abnormal for a company to have a specific political position not related to their business but not completely unheard of), but #2 is very impractical and I would argue damaging.
However, I believe the split here comes whether this is a "political issue" or a "human rights issue". In my opinion, it's human rights. And I believe any company should ensure that its employees are not fighting against equality. I guess this also ties into equality for its employees. I assume there are LGBT employees of Mozilla, and I think they must feel pretty uncomfortable right now.
Unfortunately (again, in my opinion, etc.), it's treated as a political standpoint, something that big parties can argue about. But it isn't - it's about whether LGBT individuals have the same rights as straight people.
Brendan refuses to address the issue and share his side of the story. But at least Brendan's colleague Gervase Markham at Mozilla had the guts to publicly publish and attempt to explain his hateful bigoted beliefs about gay marriage, and not censor the comments that people left on his blog, even if he ignored all the valid arguments that he had no answer to (which was most of them).
http://blog.gerv.net/2012/03/coalition-for-marriage-petition...
[1] http://projects.latimes.com/prop8/results/?position=both&...