UserChrome for hiding tab bar in conjunction with the Tree Tabs extension

userChrome.css

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

/* Hide all tabs (but not tab bar) when windowed. Preserves area for window controls (tested on macOS). */
/*#TabsToolbar { 
  visibility: collapse !important;
}*/

/* Hide the whole tab bar in fullscreen */
#TabsToolbar[inFullscreen] { 
  visibility: collapse !important; 
}

#nav-bar{
    padding-top: 0 !important;
    padding-bottom: 0 !important;
}

/* Make private Browsing icon visible */
#main-window[sizemode="maximized"][privatebrowsingmode=temporary] #private-browsing-indicator-titlebar > .private-browsing-indicator {
  z-index: 1;
}

/* Hide sidebar header */
#sidebar-header { visibility: collapse !important; }

/* Decrease sidebar header text size */
#sidebar-switcher-target { font-size: 75%; }

#sidebar {
  scrollbar-width: thin;
}

/* https://www.reddit.com/r/FirefoxCSS/comments/73iqgm/how_to_show_only_the_domain_in_the_address_bar/ */
/* https://gist.github.com/hensm/f1e28acd25e072acb63867ba6bc7b365 */
/* Place bindings.xml in the same folder as userChrome.css */
/* #urlbar {
  -moz-binding: url("bindings.xml#urlbar") !important;
} */

/*#titlebar {margin-bottom: -20px !important;}*/
#tabbrowser-tabs {visibility: collapse !important;}

#titlebar-buttonbox { 
  position: relative !important;
  overflow-x: hidden !important;
  height: 10px !important;
  -moz-transition: all .2s ease-out .2s !important;
}
  
#titlebar-buttonbox:hover {
  margin-top: -15px !important;
  margin-bottom: 5px !important;
  height: 60px !important;	
}

[privatebrowsingmode="temporary"] #titlebar {margin-bottom: 0px !important;} 
[privatebrowsingmode="temporary"] #titlebar-buttonbox {
  height: 30px !important; 
  -moz-transition: none !important;
}
[privatebrowsingmode="temporary"] #titlebar-buttonbox:hover {
  margin-top: 0px !important;
  margin-bottom: 0px !important;
  height: 30px !important;
}

[privatebrowsingmode="temporary"] #TabsToolbar {
	visibility: collapse !important;
}
[privatebrowsingmode="temporary"] #titlebar-spacer {
  background-image: url("chrome://browser/skin/private-browsing.svg");
  background-repeat: no-repeat;
  background-position: right;
}