Bug 879616 - adjust close icons for OS X to deal with bright lightweight themes, r=MattN

--HG--
extra : rebase_source : b51f2975a66704ab75f21582eee56fc797b32ba0

browser/themes/osx/browser.css

@@ -2824,10 +2824,18 @@ toolbarbutton.chevron > .toolbarbutton-menu-dropmarker {
   cursor: default;
 }
 
+.tab-close-button.close-icon:not([selected=true]):not(:hover):-moz-lwtheme-brighttext {
+  -moz-image-region: rect(0, 64px, 16px, 48px);
+}
+
 @media (min-resolution: 2dppx) {
   .tab-close-button > .toolbarbutton-icon {
     width: 16px;
   }
+
+  .tab-close-button.close-icon:not([selected=true]):not(:hover):-moz-lwtheme-brighttext {
+    -moz-image-region: rect(0, 128px, 32px, 96px);
+  }
 }
 
 .tabbrowser-arrowscrollbox > .scrollbutton-up,