One feature I miss in mainstream browsers like Chrome is the ability to completely disable tabs, leaving the window manager in control of browser windows. This is very valuable for advanced users of tiling WM that seek to automate as much of their workflow as possible.

I've tried a couple of extensions that "pull" tabs out of the parent window, but it never worked perfectly.

If Firefox had native support for this (apparently simple) feature, I believe it would gain the preference of many users of tiling window managers.