I chose Firefox as default browser only because I personally prioritize granular ad-blocking and the ability to use my own userscripts with Tampermonkey, over the native security hardening like site isolation. I still use Vanadium if I need more security.
I also use all 3 available Firefoxes, so although each may not isolate each as well as Vanadium, but separate apps are certainly isolated from each other. That does require habit changes, so you are not just opening a bunch of tabs in one browser. The default browser (A), Logged in websites (B), Grey area sites (C). For (B), try not to click links to unknown sites, crank up restrictions (don't even allow javascript), whitelist your frequented sites. Qubes is similar in its method of isolation, although for desktop they have a browser addon that will auto-open links in another VM if not whitelisted.
In Android, you can set different URLs to open in different browsers. But that doesn't work if you're already in browser.
