As someone that likes to use open tabs as a sort of todo list, I can't live without that extension. Allows me to keep different trees open for various purposes: PRs in one tree, Issues in another, academic/scientific paper to-read list, forum posts, etc

    $ cat userChrome.css 
    /* Mozilla chrome (UI) styling */

    /* Hide tabs bar
     *
     * Fri Nov 17 12:23:47 CST 2017
     * https://superuser.com/questions/1268732/how-to-hide-tab-bar-tabstrip-in-firefox-57-quantum
     * https://www.ghacks.net/2017/09/27/tree-style-tab-is-a-webextension-now/
     */

    #tabbrowser-tabs { visibility: collapse !important; }

``` #main-window:not([customizing]):not([tabsintitlebar="true"]) #toolbar-menubar[inactive="true"] + #TabsToolbar { visibility: collapse !important; } ```

This snippet shows tabs when in "customize" mode, so you can access elements from addons placed on the tab bar by default. It also shows tabs when the menubar is showing: tap alt to peek, enable menubar to have vanilla access to tabs again. Finally, if you use the setting "tabs in titlebar", tabs are not disabled.

Doing it this way enforces sensible behavior and gives you escape hatches that don't require editing CSS and restarting the browser.

My userChrome.css looks like this https://github.com/dngray/ghacks-user.js/tree/fx-desktop#use...

    @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

    /* Remove default items from the urlbar-container */
    #back-button,
    #forward-button,
    #stop-reload-button,
    #reload-button,
    #customizableui-special-spring1,
    #home-button,
    #customizableui-special-spring2,
    #library-button,
    #sidebar-button {
        display:none;
    }

    /* Disable Tab toolbar for Tree Style Tab */
    #tabbrowser-tabs {
        visibility: collapse !important;
    }

    #sidebar-header {
        display: none;
    }