background-image menu mozilla firefox 25.0.1

when I apply this to my CSS theme customizr the slider does not work on Mozilla firefox.

.tc-header {height:50px;
background-image: -webkit-linear-gradient(bottom, #1b1b1c 0%, #555860 100%);

	background-image:    -moz-linear-gradient(bottom, #1b1b1c 0%, #555860 100%);
	background-image:     -ms-linear-gradient(bottom, #1b1b1c 0%, #555860 100%);
	background-image:      -o-linear-gradient(bottom, #1b1b1c 0%, #555860 100%);
	background-image:         linear-gradient(bottom, #1b1b1c 0%, #555860 100%);
border-bottom: 0px;
border-top: 0px;
z-index: 200;
}

they send me this error message(firebug):
“Warning: Enabling the Script panel causes a Firefox slow-down due to a platform bug. This will be fixed with the next major Firefox and Firebug versions.”
While it works perfectly on all browsers and also on firefox before I apply this CSS