--- a/dom/apps/src/Webapps.js
+++ b/dom/apps/src/Webapps.js
@@ -176,27 +176,20 @@ WebappsRegistry.prototype = {
                                                appId: this._window.document.nodePrincipal.appId,
                                                oid: this._id,
                                                requestID: this.getRequestId(request) });
     return request;
   },
 
   checkInstalled: function(aManifestURL) {
     let manifestURL = Services.io.newURI(aManifestURL, null, this._window.document.baseURIObject);
+    this._window.document.nodePrincipal.checkMayLoad(manifestURL, true, false);
 
     let request = this.createRequest();
 
-    try {
-      this._window.document.nodePrincipal.checkMayLoad(manifestURL, true,
-                                                       false);
-    } catch (ex) {
-      Services.DOMRequest.fireErrorAsync(request, "CROSS_ORIGIN_CHECK_NOT_ALLOWED");
-      return request;
-    }
-
     this.addMessageListeners("Webapps:CheckInstalled:Return:OK");
     cpmm.sendAsyncMessage("Webapps:CheckInstalled", { origin: this._getOrigin(this._window.location.href),
                                                       manifestURL: manifestURL.spec,
                                                       oid: this._id,
                                                       requestID: this.getRequestId(request) });
     return request;
   },
 

--- a/dom/tests/mochitest/webapps/file_bug_779982.html
+++ b/dom/tests/mochitest/webapps/file_bug_779982.html
@@ -29,26 +29,21 @@
             finish(!this.result);
           } else {
             finish(!!this.result);
           }
         }
         break;
 
       case "checkInstalledWrong":
-        var request = navigator.mozApps.checkInstalled('http://something.org/manifest.webapp');
-        request.onsuccess = function() {
+        try {
+          navigator.mozApps.checkInstalled('http://something.org/manifest.webapp');
           finish(false);
-        }
-        request.onerror = function() {
-          if (this.error.name == "CROSS_ORIGIN_URL_NOT_ALLOWED") {
-            finish(true);
-          } else {
-            finish(false);
-          }
+        } catch (e) {
+          finish(true);
         }
         break;
 
       default:
         finish(false);
         break;
     }
   </script>