I've had the exact same experience you described. Realizing i3 is the way to go and apps shouldn't manage tabs themselves - trying to stop Firefox / Chrome from doing so - realizing it's not simple and the no tabs extension is problematic. Trying qutebrowser and giving up because it's limited.

I've settled on NoTabs Firefox with a userChrome.css that hides the tab bar until Firefox someday supports native no tabs.