No, it is not going back to XUL. But, it is amomg other things to make a function available that will remove the top tab bar or at least make it invisible. No

No, it is not going back to XUL. But, it is amomg other things to make a function available that will remove the top tab bar or at least make it invisible. Not exactly hard, I do it manually every single time I restart my Firefox Developer edition. (Yes, the chrome (i.e. frame) around the browser window is still written in markup. I go into it with inspector and enter display:none at the right place.)