Vivaldi is just Chrome. Opera is just Chrome.
Firefox forks just simply don't have the manpower to update as rapidly as browsers need updating on the web today.
So your only real option right now is Firefox unless you just want a differently skinned Google browser, or a less-secure Firefox fork.
Firefox has containers you can make to keep accounts separate, and colors your tab based on the container it's using.
https://addons.mozilla.org/en-US/firefox/addon/multi-account-containers/