Bug 1178193 - [Rule View] Tweak add rule button to only have a hover opacity when button is not disabled r=pbrosset

browser/themes/shared/devtools/ruleview.css

@@ -292,7 +292,7 @@
   opacity: 0.8;
 }
 
-#ruleview-add-rule-button:hover,
+#ruleview-add-rule-button:not([disabled]):hover,
 #pseudo-class-panel-toggle:hover,
 #pseudo-class-panel-toggle[checked] {
   opacity: 1;