Firefox userChrome.css

userChrome.css

/**
* Hide the default tabs toolbar
* I manage tabs as a sidebar using Sidebery addon: https://addons.mozilla.org/en-US/firefox/addon/sidebery/
*/
#main-window[tabsintitlebar="true"] #TabsToolbar > .toolbar-items {
  opacity: 0;
  pointer-events: none;
}
#main-window:not([tabsintitlebar="true"]) #TabsToolbar {
    visibility: collapse !important;
}

/**
* Move sidebar header to bottom
*/
#sidebar-box {
  display: flex;
  flex-direction: column-reverse;
}
#sidebar-box #sidebar {
  flex: 1 100%;
  width: 100% !important;
  max-width: unset !important;
  
}
#sidebar-box #sidebar-header {
  padding: 0 !important;
  font-size: 14px !important;
}
#sidebar-box #sidebar-header #sidebar-close {
  display: none;
}