Bug 814099 - Paused downloads don't behave properly in Downloads Panel after the session is restored. r=mak.

browser/components/downloads/src/DownloadsCommon.jsm

@@ -753,7 +753,21 @@ const DownloadsData = {
     dataItem.startTime = Math.round(aDownload.startTime / 1000);
     dataItem.currBytes = aDownload.amountTransferred;
     dataItem.maxBytes = aDownload.size;
-    dataItem.download = aDownload;
+
+    // When a download is retried, we create a different download object from
+    // the database with the same ID as before. This means that the nsIDownload
+    // that the dataItem holds might now need updating.
+    //
+    // It's possible, however, that dataItem.download is still a lazy getter
+    // if we never read the download property after initializing the dataItem
+    // from a data row in the downloads database. In that case, we can leave
+    // it alone - the next time the download property is accessed, the right
+    // download object will be retrieved.
+    let downloadIsGetter = Object.getOwnPropertyDescriptor(dataItem, "download")
+                                 .value === undefined;
+    if (!downloadIsGetter) {
+      dataItem.download = aDownload;
+    }
 
     this._views.forEach(
       function (view) view.getViewItem(dataItem).onStateChange()