Yeah, I’m not the biggest fan of Mitchell Baker spinning out Rust and Servo and the decisions she’s made about Firefox funding. She oversaw a decline of browser share from 30% to 3% and still gave herself a raise. That said, with its containers extension and other extensions, it’s still easily the most privacy focused browser I’ve seen. I like Vivaldi as a Blink/Chromium back up. Only now do I think Safari’s kind of mimicking the containers sandboxing extension by creating profiles.
I don’t do web development (yet), but have you tried Firefox Developer Edition ( I first downloaded it to try out the Rust Quantum speed up before it was available in mainline Firefox)? Is it any different than standard Firefox and if so is it any good?