@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
@-moz-document url-prefix('chrome://'){
  #navigator-toolbox #back-button,#navigator-toolbox #forward-button,
  #nav-bar #back-button,#nav-bar #forward-button{border:0}
  #navigator-toolbox #back-button>.toolbarbutton-icon,#navigator-toolbox #forward-button>.toolbarbutton-icon,#navigator-toolbox[iconsize="large"] #forward-button>.toolbarbutton-icon,
  #nav-bar #back-button>.toolbarbutton-icon,#nav-bar #forward-button>.toolbarbutton-icon,#nav-bar[iconsize="large"] #forward-button>.toolbarbutton-icon{transition:1s ease-out!important}
  #navigator-toolbox[iconsize="small"] #back-button[disabled]>.toolbarbutton-icon,#navigator-toolbox[iconsize="small"] #forward-button[disabled]>.toolbarbutton-icon,
  #nav-bar[iconsize="small"] #back-button[disabled]>.toolbarbutton-icon,#nav-bar[iconsize="small"] #forward-button[disabled]>.toolbarbutton-icon{width:10px!important}
  #navigator-toolbox[iconsize="large"] #back-button[disabled]>.toolbarbutton-icon,#navigator-toolbox[iconsize="large"] #forward-button[disabled]>.toolbarbutton-icon,
  #nav-bar[iconsize="large"] #back-button[disabled]>.toolbarbutton-icon,#nav-bar[iconsize="large"] #forward-button[disabled]>.toolbarbutton-icon{width:24px!important}
}