The chief executive of Mozilla, the company behind the Firefox web browser, has refused to rule out donating more money to anti-equal marriage campaigners.

“I don’t want to do hypotheticals,” Brendan Eich said. “I haven’t thought about that issue and I really don’t want to speculate because it’s not relevant.”

It was revealed in 2012 that Mr Eich donated $1,000 (£605) in 2008 to the campaign supporting California’s Proposition 8, whilst he was Mozilla’s chief technology officer.

The Prop 8 law banned same-sex marriages in the state and was finally struck down by the US Supreme Court after years of legal battles in June 2013.

“So I don’t want to talk about my personal beliefs because I kept them out of Mozilla all these 15 years we’ve been going,” he told The Guardian on Tuesday. “I don’t believe they’re relevant.”

The Mozilla co-founder blasted dating website OKCupid for urging its members to boycott the Firebox web browser over last month’s appointment of Mr Eich as Mozilla CEO.

Mr Eich said OkCupid’s decision was “rash” and defended his donation.

“I agree with people who say it wasn’t private, but it was personal,” he said of the donation. “But the principle that I have operated by, that is formalised in our code of conduct at Mozilla, is it’s really about keeping anything that’s not central to our mission out of our office.

“If I stop doing that now I think I would be doing wrong that code of conduct and doing a disservice to Mozilla. And I really do think it’s an important principle of inclusiveness for Mozilla to succeed.”

The first week of Mr Eich’s tenure has been marked by a series of public statements by Mozilla staff protesting his appointment and the resignation of three of Mozilla’s directors.

“With the board of directors departures, two of them were already planning to depart … those are before any of the current news about me came out,” Mr Eich said. “I would also say that OkCupid is a good example. I think there’s a chance that we could actually turn that around. I think they acted a little rashly.

“I don’t think they were aware of the statement [Mozilla foundation chair] Mitchell Baker made at the weekend [that] Mozilla as an organisation believes in LGBT equality, and I’ve heard from a lot of people that OkCupid had actually not been aware of that. So I think we can actually turn that around.”

“So far we’ve been able to bring people together of diverse beliefs including on things like marriage equality,” he said. “We couldn’t have done this, we couldn’t have done Firefox One. I would’ve been excluded, someone else would’ve been excluded because of me – I wouldn’t have done that personally, they’d have just left. So imagine a world without Firefox: not good.”

Mr Eich stressed that Firefox worked globally, including in countries like Indonesia with “different opinions”, and he said equal marriage was “not considered universal human rights yet, and maybe they will be, but that’s in the future, right now we’re in a world where we have to be global to have effect”.

The CEO refused to be drawn on whether he would donate to a Proposition 8 style campaign again in the future. “I don’t want to do hypotheticals,” he said. “I haven’t thought about that issue and I really don’t want to speculate because it’s not relevant.”

“I think I’m the best person for the job and I’m doing the job,” he added.