Arc is Chromium based. In other words, you’re still using Chrome/Chromium.
Firefox and Safari are the only two browsers (seemingly) left on the market with their own rendering engines. (Gecko and WebKit respectively)
So while things are fucking bad at Mozilla, it’s important to try to get people to use Firefox so market share will increase enough that Mozilla won’t want to diversify away from Firefox. I know that’s living on hopes and dreams, but that’s better than just rolling over and letting Google take over the modern world-wide web.