As the force behind Firefox, the internet’s leading open-source browser, the Mozilla Foundation tends to be associated with progressive values. So its appointment this week of a CEO who donated to a campaign that opposed gay marriage has caused ripples among Firefox developers and the browser’s fans.

Some Mozilla developers said they would boycott the foundation after the promotion of Brendan Eich to the top position. Eich donated $1,000 to the Proposition 8 campaign in California, which succeeded in banning same-sex marriage in the state for almost five years.

“As a gay couple who were unable to get married in California until recently, we morally cannot support a Foundation that would not only leave someone with hateful views in power, but will give them a promotion and put them in charge of the entire organization,” said developer Hampton Catlin, who founded the tech firm Rarebit with his husband Michael Lintorn Catlin.

In a blog post on Rarebit’s site, Catlin said he understood that not everyone at Mozilla has displayed opposition to same-sex marriage, but that he believes the choice for a CEO sent an important symbolic message.

“Their ideas, beliefs, philosophies, and personalities drive organizations,” Catlin said. “And, when it’s an organization that I’m personally investing in, it’s even more important.”

Eich's $1,000 donation to support Prop 8 was first disclosed in 2012 and he responded to the renewed criticism in his personal blog on Wednesday. He said he wanted to reassert his commitment "to fostering equality and welcome for LGBT individuals at Mozilla" and outlined how he hopes to do that.

"I know some will be skeptical about this, and that words alone will not change anything," Eich said. "I can only ask for your support to have the time to 'show, not tell'; and in the meantime express my sorrow at having caused pain."

As part of the post, Eich announced the launch of a new Mozilla initiative, Project Ascend. Created by Mozilla employee Lukas Blakk, the initiative seeks to create an Open Source hacking course targeted at underrepresented populations.

Christie Koehler, an employee of Mozilla who identifies herself as queer and is also working on Project Ascend, said she was disappointed when she learned about the campaign donation, but accepted that sometimes people have to work with people who have contradictory beliefs to their own.

“The key is to figure out when it’s important to walk away from interacting with a person or community because of a misalignment in beliefs, and when you need to set aside the disagreement and commit to working together in service of the shared goal,” Koehler wrote in a blog post.

She also said Mozilla employees tend to have progressive leanings, and that she has not personally experienced discriminatory behavior from Eich in the Mozilla workplace. “To be clear, I’m personally disappointed about Brendan’s donation,” Koehler said. “However, aside from how it affected me emotionally, I have nothing to indicate that it’s materially hurt my work within the Mozilla community or as a Mozilla employee.”

Following the renewed criticism, Mozilla posted a statement on the company’s website.

“Mozilla has always been deeply committed to honoring diversity in sexual orientation and beliefs within our staff and community, across all the project’s activities,” Mozilla said.

Mozilla cited its health benefit policies as an example of how it honors sexual diversity, because it offers the same benefits to domestic partnerships as it does to married couples and its life insurance policy covers domestic partnerships as well.

“With thousands of people spanning many countries and cultures, diversity is core to who we are, and we’re united in our mission to keep the Web open and accessible for everyone,” Mozilla said.

Mozilla began as an open source project at Netscape in 1998 and is a non-profit foundation to create open source products including the hugely popular Firefox browser. Firefox is thought to be the third most popular browser in the world, and is used by half a billion people, according to the organization.

Google has been Mozilla's primary funder since 2006 and was responsible for more than 90% of the organization's revenue in 2012. The search giant now pays Mozilla $300m per year to be the default search engine option for Firefox.