Убираем скроллбар: ‰ cat ~/.mozilla/firefox/i3daxy5h.default/chrome/userChrome.css
@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

content browser {

margin-right: -14px !important;
overflow-y: scroll;
overflow-x: hidden;
}