tree-style tab setup
How to get rid of the top bar in firefox after installing tree style tab:
In about:config (accept the risk), search toolkit.legacyUserProfileCustomizations.stylesheets and hit the funny looking button to toggle it to true.
In about:support, above the fold in the “Application Basics” section, find Profile Directory.
In that directory, mkdir chrome, then create userChrome.css, containing:
#main-window[tabsintitlebar="true"]:not([extradragspace="true"]) #TabsToolbar
{
opacity: 0;
pointer-events: none;
}
#main-window:not([tabsintitlebar="true"]) #TabsToolbar {
visibility: collapse !important;
}