userContent.css

@-moz-document url(about:home), url(about:newtab), url(about:blank)
{
  html
	{
	background: url(111.png) center center no-repeat !important;
	background-size: 450px !important;
	width:100%; height:100%;
	background-color: #1f1f1f !important;
	}
  body
	{
	display:none;
	}
}