fix -moz-background-clip value so that old Firefox can understand. Fix for jquery-archive#2677

Author: myakura

themes/valencia/jquery.mobile.theme.css

@@ -874,7 +874,7 @@ a.ui-link-inherit {
 .ui-btn-corner-br, .ui-btn-corner-top, .ui-btn-corner-bottom, 
 .ui-btn-corner-right, .ui-btn-corner-left, .ui-btn-corner-all {
   -webkit-background-clip: padding-box;
-     -moz-background-clip: padding-box;
+     -moz-background-clip: padding;
           background-clip: padding-box;
 }
 
@@ -965,4 +965,4 @@ a.ui-btn.ui-btn-inline.ui-btn-corner-all .ui-btn-inner{
 /* inner highlight is janky! */
 .ui-dialog a.ui-btn-icon-notext.ui-btn-corner-all .ui-btn-inner.ui-btn-corner-all{
   border-top-color: transparent; 
-}
+}