While a handful of workers at top tech firms including Apple, Yahoo and Google supported the gay-marriage ban, the vast majority gave money to oppose it.
Mozilla Chairwoman Mitchell Baker touched on the delicate balancing act in her Thursday blog post announcing Eich's resignation.
"Mozilla believes both in equality and freedom of speech," Baker said. "Equality is necessary for meaningful speech. And you need free speech to fight for equality. Figuring out how to stand for both at the same time can be hard."
Mozilla, which is based in Mountain View, Calif., declined to make any further comment Friday. Eich did not respond to requests for comment.
Harmeet Dhillon, vice chairman of the California Republican Party, said Silicon Valley can be intolerant, and noted 52 percent of California voters supported the anti-gay marriage measure.
"Many people have told me they're afraid to identify themselves as conservatives," she said. "We face issues of political correctness all the time."
Eich's resignation should serve as a chilling reminder to workers at all levels that their off-duty behavior or personal opinions could still cost them their jobs if their employers are worried about a backlash hurting their business, said Lewis Maltby, president of the National Workrights Institute.
New York and a few other states prohibit employers from firing workers for political activity, but even those protections are limited.
Some firings of lower-level employees have raised even more troubling questions about worker rights than Eich's resignation, Maltby said. Some women have gotten fired for Facebook pictures showing them wearing a bikini on the beach, and a teacher lost her job for another Facebook photo that showed her holding a beer.