Followup fix for bug 524995, r=gavin

content/events/test/test_bug226361.xhtml

@@ -36,8 +36,10 @@ function setOrRestoreTabFocus(newValue) {
   const prefSvcIID = Components.interfaces.nsIPrefService;
   var prefs = Components.classes[prefSvcContractID].getService(prefSvcIID)
                                                    .getBranch("accessibility.");
-  if (!newValue && prefs.prefHasUserValue("tabfocus")) {
-    prefs.clearUserPref("tabfocus");
+  if (!newValue) {
+    if (prefs.prefHasUserValue("tabfocus")) {
+      prefs.clearUserPref("tabfocus");
+    }
   } else {
     prefs.setIntPref("tabfocus", newValue);
   }

content/xul/content/test/test_bug486990.xul

@@ -93,8 +93,10 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=486990
     var prefs = Components.classes[prefSvcContractID].getService(prefSvcIID)
                                                      .getBranch("dom.event.contextmenu.");
     try {
-      if (allow && prefs.prefHasUserValue("enabled")) {
-        prefs.clearUserPref("enabled");
+      if (allow) {
+        if (prefs.prefHasUserValue("enabled")) {
+          prefs.clearUserPref("enabled");
+        }
       } else {
         prefs.setBoolPref("enabled", allow);
       }