Bug 759065 - Fall back to downloading the full update if staging the update in the background fails; r=rstrong

browser/base/content/aboutDialog.js

@@ -482,6 +482,13 @@ appUpdater.prototype =
       return;
     }
 
+    this.setupDownloadingUI();
+  },
+
+  /**
+   * Switches to the UI responsible for tracking the download.
+   */
+  setupDownloadingUI: function() {
     this.downloadStatus = document.getElementById("downloadStatus");
     this.downloadStatus.value =
       DownloadUtils.getTransferTotal(0, this.update.selectedPatch.size);
@@ -527,7 +534,7 @@ appUpdater.prototype =
         let self = this;
         Services.obs.addObserver(function (aSubject, aTopic, aData) {
           // Update the UI when the background updater is finished
-          let status = update.state;
+          let status = aData;
           if (status == "applied" || status == "applied-service" ||
               status == "pending" || status == "pending-service") {
             // If the update is successfully applied, or if the updater has
@@ -540,6 +547,12 @@ appUpdater.prototype =
             // Background update has failed, let's show the UI responsible for
             // prompting the user to update manually.
             self.selectPanel("downloadFailed");
+          } else if (status == "downloading") {
+            // We've fallen back to downloading the full update because the
+            // partial update failed to get staged in the background.
+            // Therefore we need to keep our observer.
+            self.setupDownloadingUI();
+            return;
           }
           Services.obs.removeObserver(arguments.callee, "update-staged");
         }, "update-staged", false);