Windows Firefox userChrome.css

userChrome.css

/* about:config - enable toolkit.legacyUserProfileCustomizations.stylesheets */

/* To hide horizontal bars */
#main-window[tabsintitlebar="true"]:not([extradragspace="true"]) #TabsToolbar {
    display: none;
}

#main-window:not([tabsintitlebar="true"]) #TabsToolbar {
    visibility: collapse !important;
}

/* For Tree Style Tab */
#sidebar-header{
    display: none;
}