You may want to have no address or tab bar given that you enter URLs in a Tridactyl's own field, and you manage tabs as buffers. Even worse, Firefox own address bar steals focus in some scenarios.

The worst part now is the "no extensions on special pages" and "no extension may open an about:* page".

edit: Nevermind. I was just using the wrong hack. Using this one: https://news.ycombinator.com/item?id=15870894 + using Customize to reenable the title bar works great.

  #TabsToolbar {
        visibility: collapse !important;
      }

  /* to hide the native top tabs */
  #TabsToolbar * {
      visibility: collapse;
  }
  /* to give the top toolbar a bit of height so the window controls don't dangle off to the right */
  #TabsToolbar:before {
    content: '';
    display: block;
    width: 100%;
    height: 20px;
  }

  /* to hide the sidebar header */
  #sidebar-header {
      visibility: collapse;
  }

#TabsToolbar {visibility: collapse;}

#titlebar {margin:0px !important; display:none}

#sidebar-header {visibility: collapse;}

#nav-bar-customization-target {margin-top:10px;}

I use this with titlebar disabled

Also, such an API would allow an extension to make the browser UI unusable, which would make figuring out the problem and removing the offending extension quite hard.

There are no security reasons for not having such a setting. None.

I doubt that's the reason.

https://bugzilla.mozilla.org/show_bug.cgi?id=1332447

This comment kinda sums up why it's a hard problem https://bugzilla.mozilla.org/show_bug.cgi?id=1332447#c116

There's a major problem with addons doing stuff the users don't want, and the tab strip is a critical portion of the user interface so "just let them hide it" has problems with abuse. So it needs to be something that can still be autoreviewed, and it needs to be something that gives clear indications to the user as to what is going on.