@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);
 
@-moz-document url(chrome://browser/content/browser.xul) {
    #main-window[tabsintitlebar]:not([sizemode=fullscreen]) #TabsToolbar:not(:-moz-lwtheme)::after {
        box-shadow: 0 0 0 0 !important;
    }
}