According to your link below he was co-founder of Mozilla in 1998. Based on the other information on that page, he had a very significant role in shaping Mozilla and their tools, so as disagreeable as his personal views may be, it’s not impossible that Firefox might not even exist today were it not for his work there.

Someone else has already pointed out that he was pushed out, but he actually resigned due to public pressure (he was only CEO for 11 days, and one of the board members even left due to him being appointed) before going on to found Brave and becoming the CEO there lol.

If I chose not to use products based on the personal beliefs of the people who worked on them I don’t think I’d have very many options. Mozilla has made heaps of questionable decisions over the years, but the other options are generally much worse.