I wish tabless mode would get more love from browser developers. It was the default design choice for years before tabs showed up.
From what I can tell, tabbed browsing was/is popular because the default window managers of popular operating systems are underpowered. On Windows, it's not possible to tab arbitrary application windows without third-party software like TidyTabs or Groupy.
In my opinion, the window manager should be taking care of things like tabbing, rather than the application. This way, it becomes easy to group windows together based on their purpose rather than by the fact that they're spawned by the same application.
For this reason, I've grown very fond of i3wm because it makes tabbing and grouping so simple.
Getting back on topic, I've had little success finding browsers with decent tabless modes. None of the config tweaks I found for enabling tabless mode on Firefox worked correctly. For a while, I tried qutebrowser and enjoyed its keyboard-driven interface, but ran into various usability issues that made me go back to Firefox.
(Originally posted at Hacker News.)