[PALEMOON] Bug 1117141 - Part 2 of 2 - Refactor notifications and remove the DownloadsDataItem object

4 files changed, 234 insertions, 593 deletions

diff --git a/application/palemoon/components/downloads/DownloadsCommon.jsm b/application/palemoon/components/downloads/DownloadsCommon.jsm
index c2185f623..e110aa904 100644
--- a/application/palemoon/components/downloads/DownloadsCommon.jsm
+++ b/application/palemoon/components/downloads/DownloadsCommon.jsm
@@ -8,7 +8,6 @@
 
 this.EXPORTED_SYMBOLS = [
   "DownloadsCommon",
-  "DownloadsDataItem",
 ];
 
 /**
@@ -22,14 +21,9 @@ this.EXPORTED_SYMBOLS = [
  *
  * DownloadsData
  * Retrieves the list of past and completed downloads from the underlying
- * Download Manager data, and provides asynchronous notifications allowing
+ * Downloads API data, and provides asynchronous notifications allowing
  * to build a consistent view of the available data.
  *
- * DownloadsDataItem
- * Represents a single item in the list of downloads.  This object wraps the
- * Download object from the JavaScript API for downloads.  A specialized version
- * of this object is implemented in the Places front-end view.
- *
  * DownloadsIndicatorData
  * This object registers itself with DownloadsData as a view, and transforms the
  * notifications it receives into overall status data, that is then broadcast to
@@ -399,10 +393,10 @@ this.DownloadsCommon = {
   },
 
   /**
-   * Given an iterable collection of DownloadDataItems, generates and returns
+   * Given an iterable collection of Download objects, generates and returns
    * statistics about that collection.
    *
-   * @param aDataItems An iterable collection of DownloadDataItems.
+   * @param downloads An iterable collection of Download objects.
    *
    * @return Object whose properties are the generated statistics. Currently,
    *         we return the following properties:
@@ -419,7 +413,7 @@ this.DownloadsCommon = {
    *                           complete.
    *         percentComplete : The percentage of bytes successfully downloaded.
    */
-  summarizeDownloads: function DC_summarizeDownloads(aDataItems)
+summarizeDownloads(downloads) {
   {
     let summary = {
       numActive: 0,
@@ -431,14 +425,13 @@ this.DownloadsCommon = {
       // slowestSpeed is Infinity so that we can use Math.min to
       // find the slowest speed. We'll set this to 0 afterwards if
       // it's still at Infinity by the time we're done iterating all
-      // dataItems.
+      // download.
       slowestSpeed: Infinity,
       rawTimeLeft: -1,
       percentComplete: -1
     }
 
-    for (let dataItem of aDataItems) {
-      let download = dataItem.download;
+    for (let download of downloads) {
       let state = DownloadsCommon.stateOfDownload(download);
       let maxBytes = DownloadsCommon.maxBytesOfDownload(download);
 
@@ -670,16 +663,12 @@ XPCOMUtils.defineLazyGetter(DownloadsCommon, "useJSTransfer", function () {
 function DownloadsDataCtor(aPrivate) {
   this._isPrivate = aPrivate;
 
-  // Contains all the available DownloadsDataItem objects.
-  this.dataItems = new Set();
+  // Contains all the available Download objects and their integer state.
   this.oldDownloadStates = new Map();
 
   // Array of view objects that should be notified when the available download
   // data changes.
   this._views = [];
-
-  // Maps Download objects to DownloadDataItem objects.
-  this._downloadToDataItemMap = new Map();
 }
 
 DownloadsDataCtor.prototype = {
@@ -706,12 +695,17 @@ DownloadsDataCtor.prototype = {
   },
 
   /**
+   * Iterator for all the available Download objects. This is empty until the
+   * data has been loaded using the JavaScript API for downloads.
+   */
+  get downloads() this.oldDownloadStates.keys(),
+
+  /**
    * True if there are finished downloads that can be removed from the list.
    */
   get canRemoveFinished()
   {
-    for (let dataItem of this.dataItems) {
-      let download = dataItem.download;
+    for (let download of this.oldDownloadStates.keys()) {
       // Stopped, paused, and failed downloads with partial data are removed.
       if (download.stopped && !(download.canceled && download.hasPartialData)) {
         return true;
@@ -734,37 +728,32 @@ DownloadsDataCtor.prototype = {
   //////////////////////////////////////////////////////////////////////////////
   //// Integration with the asynchronous Downloads back-end
 
-  onDownloadAdded: function (aDownload)
-  {
-    let dataItem = new DownloadsDataItem(aDownload);
-    this._downloadToDataItemMap.set(aDownload, dataItem);
-    this.dataItems.add(dataItem);
-    this.oldDownloadStates.set(aDownload,
-                               DownloadsCommon.stateOfDownload(aDownload));
+  onDownloadAdded(download) {
+    // Download objects do not store the end time of downloads, as the Downloads
+    // API does not need to persist this information for all platforms. Once a
+    // download terminates on a Desktop browser, it becomes a history download,
+    // for which the end time is stored differently, as a Places annotation.
+    download.endTime = Date.now();
+
+    this.oldDownloadStates.set(download,
+                               DownloadsCommon.stateOfDownload(download));
 
     for (let view of this._views) {
-      view.onDataItemAdded(dataItem, true);
+      view.onDownloadAdded(download, true);
     }
   },
 
-  onDownloadChanged: function (aDownload)
-  {
-    let aDataItem = this._downloadToDataItemMap.get(aDownload);
-    if (!aDataItem) {
-      Cu.reportError("Download doesn't exist.");
-      return;
-    }
-
-    let oldState = this.oldDownloadStates.get(aDownload);
-    let newState = DownloadsCommon.stateOfDownload(aDownload);
-    this.oldDownloadStates.set(aDownload, newState);
+  onDownloadChanged(download) {
+    let oldState = this.oldDownloadStates.get(download);
+    let newState = DownloadsCommon.stateOfDownload(download);
+    this.oldDownloadStates.set(download, newState);
 
     if (oldState != newState) {
-      if (aDownload.succeeded ||
-          (aDownload.canceled && !aDownload.hasPartialData) ||
-          aDownload.error) {
+      if (download.succeeded ||
+          (download.canceled && !download.hasPartialData) ||
+          download.error) {
         // Store the end time that may be displayed by the views.
-        aDownload.endTime = Date.now();
+        download.endTime = Date.now();
 
         // This state transition code should actually be located in a Downloads
         // API module (bug 941009).  Moreover, the fact that state is stored as
@@ -773,17 +762,17 @@ DownloadsDataCtor.prototype = {
         if (!this._isPrivate) {
           try {
             let downloadMetaData = {
-              state: DownloadsCommon.stateOfDownload(aDownload),
-              endTime: aDownload.endTime,
+              state: DownloadsCommon.stateOfDownload(download),
+              endTime: download.endTime,
             };
-            if (aDownload.succeeded ||
-                (aDownload.error && aDownload.error.becauseBlocked)) {
+            if (download.succeeded ||
+                (download.error && download.error.becauseBlocked)) {
               downloadMetaData.fileSize =
-                DownloadsCommon.maxBytesOfDownload(aDataItem.download);
+                DownloadsCommon.maxBytesOfDownload(download);
             }
   
             PlacesUtils.annotations.setPageAnnotation(
-                          NetUtil.newURI(aDownload.source.url),
+                          NetUtil.newURI(download.source.url),
                           "downloads/metaData",
                           JSON.stringify(downloadMetaData), 0,
                           PlacesUtils.annotations.EXPIRE_WITH_HISTORY);
@@ -795,41 +784,33 @@ DownloadsDataCtor.prototype = {
 
       for (let view of this._views) {
         try {
-          view.onDataItemStateChanged(aDataItem);
+          view.onDownloadStateChanged(download);
         } catch (ex) {
           Cu.reportError(ex);
         }
       }
 
-      if (aDownload.succeeded ||
-          (aDownload.error && aDownload.error.becauseBlocked)) {
+      if (download.succeeded ||
+          (download.error && download.error.becauseBlocked)) {
         this._notifyDownloadEvent("finish");
       }
     }
 
-    if (!aDownload.newDownloadNotified) {
-      aDownload.newDownloadNotified = true;
+    if (!download.newDownloadNotified) {
+      download.newDownloadNotified = true;
       this._notifyDownloadEvent("start");
     }
 
     for (let view of this._views) {
-      view.onDataItemChanged(aDataItem);
+      view.onDownloadChanged(download);
     }
   },
 
-  onDownloadRemoved: function (aDownload)
-  {
-    let dataItem = this._downloadToDataItemMap.get(aDownload);
-    if (!dataItem) {
-      Cu.reportError("Download doesn't exist.");
-      return;
-    }
+  onDownloadRemoved(download) {
+    this.oldDownloadStates.delete(download);
 
-    this._downloadToDataItemMap.delete(aDownload);
-    this.dataItems.delete(dataItem);
-    this.oldDownloadStates.delete(aDownload);
     for (let view of this._views) {
-      view.onDataItemRemoved(dataItem);
+      view.onDownloadRemoved(download);
     }
   },
 
@@ -881,12 +862,9 @@ DownloadsDataCtor.prototype = {
     //let loadedItemsArray = [dataItem
     //                        for each (dataItem in this.dataItems)
     //                        if (dataItem)];
-    let loadedItemsArray = [...this.dataItems];
-
-    loadedItemsArray.sort(function(a, b) b.download.startTime - a.download.startTime);
-    loadedItemsArray.forEach(
-      function (dataItem) aView.onDataItemAdded(dataItem, false)
-    );
+    let downloadsArray = [...this.oldDownloadStates.keys()];
+    downloadsArray.sort((a, b) => b.startTime - a.startTime);
+    downloadsArray.forEach(download => aView.onDownloadAdded(download, false));
 
     // Notify the view that all data is available unless loading is in progress.
     if (!this._pendingStatement) {
@@ -1338,254 +1316,6 @@ XPCOMUtils.defineLazyGetter(this, "DownloadsData", function() {
 });
 
 ////////////////////////////////////////////////////////////////////////////////
-//// DownloadsDataItem
-
-/**
- * Represents a single item in the list of downloads.  This object either wraps
- * an existing nsIDownload from the Download Manager, or provides the same
- * information read directly from the downloads database, with the possibility
- * of querying the nsIDownload lazily, for performance reasons.
- *
- * @param aSource
- *        Object containing the data with which the item should be initialized.
- *        This should implement either nsIDownload or mozIStorageRow.  If the
- *        JavaScript API for downloads is enabled, this is a Download object.
- */
-function DownloadsDataItem(aSource)
-{
-  this._initFromJSDownload(aSource);
-}
-
-DownloadsDataItem.prototype = {
-  get state() DownloadsCommon.stateOfDownload(this.download),
-
-  /**
-   * Initializes this object from the JavaScript API for downloads.
-   *
-   * The endTime property is initialized to the current date and time.
-   *
-   * @param aDownload
-   *        The Download object with the current state.
-   */
-  _initFromJSDownload: function (aDownload)
-  {
-    this.download = aDownload;
-    this.download.endTime = Date.now();
-  },
-
-  /**
-   * Initializes this object from a download object of the Download Manager.
-   *
-   * The endTime property is initialized to the current date and time.
-   *
-   * @param aDownload
-   *        The nsIDownload with the current state.
-   */
-  _initFromDownload: function DDI_initFromDownload(aDownload)
-  {
-    this._download = aDownload;
-
-    // Fetch all the download properties eagerly.
-    this.downloadGuid = aDownload.guid;
-    this.file = aDownload.target.spec;
-    this.target = aDownload.displayName;
-    this.uri = aDownload.source.spec;
-    this.referrer = aDownload.referrer && aDownload.referrer.spec;
-    this.state = aDownload.state;
-    this.startTime = Math.round(aDownload.startTime / 1000);
-    this.endTime = Date.now();
-    this.currBytes = aDownload.amountTransferred;
-    this.maxBytes = aDownload.size;
-    this.resumable = aDownload.resumable;
-    this.speed = aDownload.speed;
-    this.percentComplete = aDownload.percentComplete;
-  },
-
-  /**
-   * Initializes this object from a data row in the downloads database, without
-   * querying the associated nsIDownload object, to improve performance when
-   * loading the list of downloads asynchronously.
-   *
-   * When this object is initialized in this way, accessing the "download"
-   * property loads the underlying nsIDownload object synchronously, and should
-   * be avoided unless the object is really required.
-   *
-   * @param aStorageRow
-   *        The mozIStorageRow from the downloads database.
-   */
-  _initFromDataRow: function DDI_initFromDataRow(aStorageRow)
-  {
-    // Get the download properties from the data row.
-    this._download = null;
-    this.downloadGuid = aStorageRow.getResultByName("guid");
-    this.file = aStorageRow.getResultByName("target");
-    this.target = aStorageRow.getResultByName("name");
-    this.uri = aStorageRow.getResultByName("source");
-    this.referrer = aStorageRow.getResultByName("referrer");
-    this.state = aStorageRow.getResultByName("state");
-    this.startTime = Math.round(aStorageRow.getResultByName("startTime") / 1000);
-    this.endTime = Math.round(aStorageRow.getResultByName("endTime") / 1000);
-    this.currBytes = aStorageRow.getResultByName("currBytes");
-    this.maxBytes = aStorageRow.getResultByName("maxBytes");
-
-    // Now we have to determine if the download is resumable, but don't want to
-    // access the underlying download object unnecessarily.  The only case where
-    // the property is relevant is when we are currently downloading data, and
-    // in this case the download object is already loaded in memory or will be
-    // loaded very soon in any case.  In all the other cases, including a paused
-    // download, we assume that the download is resumable.  The property will be
-    // updated as soon as the underlying download state changes.
-
-    // We'll start by assuming we're resumable, and then if we're downloading,
-    // update resumable property in case we were wrong.
-    this.resumable = true;
-
-    if (this.state == nsIDM.DOWNLOAD_DOWNLOADING) {
-      this.getDownload(function(aDownload) {
-        this.resumable = aDownload.resumable;
-      }.bind(this));
-    }
-
-    // Compute the other properties without accessing the download object.
-    this.speed = 0;
-    this.percentComplete = this.maxBytes <= 0
-                           ? -1
-                           : Math.round(this.currBytes / this.maxBytes * 100);
-  },
-
-  /**
-   * Asynchronous getter for the download object corresponding to this data item.
-   *
-   * @param aCallback
-   *        A callback function which will be called when the download object is
-   *        available.  It should accept one argument which will be the download
-   *        object.
-   */
-  getDownload: function DDI_getDownload(aCallback) {
-    if (this._download) {
-      // Return the download object asynchronously to the caller
-      let download = this._download;
-      Services.tm.mainThread.dispatch(function () aCallback(download),
-                                      Ci.nsIThread.DISPATCH_NORMAL);
-    } else {
-      Services.downloads.getDownloadByGUID(this.downloadGuid,
-                                           function(aStatus, aResult) {
-        if (!Components.isSuccessCode(aStatus)) {
-          Cu.reportError(
-            new Components.Exception("Cannot retrieve download for GUID: " +
-                                     this.downloadGuid));
-        } else {
-          this._download = aResult;
-          aCallback(aResult);
-        }
-      }.bind(this));
-    }
-  },
-
-  /**
-   * Indicates whether the download is proceeding normally, and not finished
-   * yet.  This includes paused downloads.  When this property is true, the
-   * "progress" property represents the current progress of the download.
-   */
-  get inProgress()
-  {
-    return [
-      nsIDM.DOWNLOAD_NOTSTARTED,
-      nsIDM.DOWNLOAD_QUEUED,
-      nsIDM.DOWNLOAD_DOWNLOADING,
-      nsIDM.DOWNLOAD_PAUSED,
-      nsIDM.DOWNLOAD_SCANNING,
-    ].indexOf(this.state) != -1;
-  },
-
-  /**
-   * This is true during the initial phases of a download, before the actual
-   * download of data bytes starts.
-   */
-  get starting()
-  {
-    return this.state == nsIDM.DOWNLOAD_NOTSTARTED ||
-           this.state == nsIDM.DOWNLOAD_QUEUED;
-  },
-
-  /**
-   * Indicates whether the download is paused.
-   */
-  get paused()
-  {
-    return this.state == nsIDM.DOWNLOAD_PAUSED;
-  },
-
-  /**
-   * Indicates whether the download is in a final state, either because it
-   * completed successfully or because it was blocked.
-   */
-  get done()
-  {
-    return [
-      nsIDM.DOWNLOAD_FINISHED,
-      nsIDM.DOWNLOAD_BLOCKED_PARENTAL,
-      nsIDM.DOWNLOAD_BLOCKED_POLICY,
-      nsIDM.DOWNLOAD_DIRTY,
-    ].indexOf(this.state) != -1;
-  },
-
-  /**
-   * Indicates whether the download stopped because of an error, and can be
-   * resumed manually.
-   */
-  get canRetry()
-  {
-    return this.state == nsIDM.DOWNLOAD_CANCELED ||
-           this.state == nsIDM.DOWNLOAD_FAILED;
-  },
-
-  /**
-   * Returns the nsILocalFile for the download target.
-   *
-   * @throws if the native path is not valid.  This can happen if the same
-   *         profile is used on different platforms, for example if a native
-   *         Windows path is stored and then the item is accessed on a Mac.
-   *
-   * @deprecated Callers should use OS.File and "download.target.path".
-   */
-  get localFile()
-  {
-    // We should remove  should use this.download.target.partFilePath and check asyncrhonously.
-    return new FileUtils.File(this.download.target.path);
-  },
-
-  /**
-   * Returns the nsILocalFile for the partially downloaded target.
-   *
-   * @throws if the native path is not valid.  This can happen if the same
-   *         profile is used on different platforms, for example if a native
-   *         Windows path is stored and then the item is accessed on a Mac.
-   *
-   * @deprecated Callers should use OS.File and "download.target.partFilePath".
-   */
-  get partFile()
-  {
-    return new FileUtils.File(this.download.target.path + kPartialDownloadSuffix);
-  },
-
-  /**
-   * Support function that deletes the local file for a download. This is
-   * used in cases where the Download Manager service doesn't delete the file
-   * from disk when cancelling. See bug 732924.
-   */
-  _ensureLocalFileRemoved: function DDI__ensureLocalFileRemoved()
-  {
-    try {
-      let localFile = this.localFile;
-      if (localFile.exists()) {
-        localFile.remove(false);
-      }
-    } catch (ex) { }
-  }
-};
-
-////////////////////////////////////////////////////////////////////////////////
 //// DownloadsViewPrototype
 
 /**
@@ -1712,9 +1442,9 @@ const DownloadsViewPrototype = {
    * Called when a new download data item is available, either during the
    * asynchronous data load or when a new download is started.
    *
-   * @param aDataItem
-   *        DownloadsDataItem object that was just added.
-   * @param aNewest
+   * @param download
+   *        Download object that was just added.
+   * @param newest
    *        When true, indicates that this item is the most recent and should be
    *        added in the topmost position.  This happens when a new download is
    *        started.  When false, indicates that the item is the least recent
@@ -1723,46 +1453,47 @@ const DownloadsViewPrototype = {
    *
    * @note Subclasses should override this.
    */
-  onDataItemAdded: function DVP_onDataItemAdded(aDataItem, aNewest)
-  {
+  onDownloadAdded(download, newest) {
     throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
   },
 
   /**
-   * Called when a data item is removed, ensures that the widget associated with
-   * the view item is removed from the user interface.
+   * Called when the overall state of a Download has changed. In particular,
+   * this is called only once when the download succeeds or is blocked
+   * permanently, and is never called if only the current progress changed.
    *
-   * @param aDataItem
-   *        DownloadsDataItem object that is being removed.
+   * The onDownloadChanged notification will always be sent afterwards.
    *
    * @note Subclasses should override this.
    */
-  onDataItemRemoved: function DVP_onDataItemRemoved(aDataItem)
-  {
+  onDownloadStateChanged(download) {
     throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
   },
 
   /**
-   * Called when the "state" property of a DownloadsDataItem has changed.
+   * Called every time any state property of a Download may have changed,
+   * including progress properties.
    *
-   * The onDataItemChanged notification will be sent afterwards.
+   * Note that progress notification changes are throttled at the Downloads.jsm
+   * API level, and there is no throttling mechanism in the front-end.
    *
    * @note Subclasses should override this.
    */
-  onDataItemStateChanged(aDataItem) {
+  onDownloadChanged(download) {
+  {
     throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
   },
 
   /**
-   * Called every time any state property of a DownloadsDataItem may have
-   * changed, including progress properties and the "state" property.
+   * Called when a data item is removed, ensures that the widget associated with
+   * the view item is removed from the user interface.
    *
-   * Note that progress notification changes are throttled at the Downloads.jsm
-   * API level, and there is no throttling mechanism in the front-end.
+   * @param download
+   *        Download object that is being removed.
    *
    * @note Subclasses should override this.
    */
-  onDataItemChanged(aDataItem) {
+  onDownloadRemoved(download) {
     throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
   },
 
@@ -1826,9 +1557,6 @@ DownloadsIndicatorDataCtor.prototype = {
   //////////////////////////////////////////////////////////////////////////////
   //// Callback functions from DownloadsData
 
-  /**
-   * Called after data loading finished.
-   */
   onDataLoadCompleted: function DID_onDataLoadCompleted()
   {
     DownloadsViewPrototype.onDataLoadCompleted.call(this);
@@ -1845,42 +1573,13 @@ DownloadsIndicatorDataCtor.prototype = {
     this._itemCount = 0;
   },
 
-  /**
-   * Called when a new download data item is available, either during the
-   * asynchronous data load or when a new download is started.
-   *
-   * @param aDataItem
-   *        DownloadsDataItem object that was just added.
-   * @param aNewest
-   *        When true, indicates that this item is the most recent and should be
-   *        added in the topmost position.  This happens when a new download is
-   *        started.  When false, indicates that the item is the least recent
-   *        with regard to the items that have been already added. The latter
-   *        generally happens during the asynchronous data load.
-   */
-  onDataItemAdded: function DID_onDataItemAdded(aDataItem, aNewest)
+  onDownloadAdded(download, newest) {
   {
     this._itemCount++;
     this._updateViews();
   },
 
-  /**
-   * Called when a data item is removed, ensures that the widget associated with
-   * the view item is removed from the user interface.
-   *
-   * @param aDataItem
-   *        DownloadsDataItem object that is being removed.
-   */
-  onDataItemRemoved: function DID_onDataItemRemoved(aDataItem)
-  {
-    this._itemCount--;
-    this._updateViews();
-  },
-
-  // DownloadsView
-  onDataItemStateChanged(aDataItem) {
-    let download = aDataItem.download;
-
+  onDownloadStateChanged(download) {
     if (download.succeeded || download.error) {
       this.attention = true;
     }
@@ -1890,8 +1589,12 @@ DownloadsIndicatorDataCtor.prototype = {
     this._lastTimeLeft = -1;
   },
 
-  // DownloadsView
-  onDataItemChanged() {
+  onDownloadChanged(download) {
+    this._updateViews();
+  },
+
+  onDownloadRemoved(download) {
+    this._itemCount--;
     this._updateViews();
   },
 
@@ -1983,22 +1686,17 @@ DownloadsIndicatorDataCtor.prototype = {
   _lastTimeLeft: -1,
 
   /**
-   * A generator function for the dataItems that this summary is currently
+   * A generator function for the Download objects this summary is currently
    * interested in. This generator is passed off to summarizeDownloads in order
-   * to generate statistics about the dataItems we care about - in this case,
-   * it's all dataItems for active downloads.
+   * to generate statistics about the downloads we care about - in this case,
+   * it's all active downloads.
    */
-  _activeDataItems: function DID_activeDataItems()
-  {
-    let dataItems = this._isPrivate ? PrivateDownloadsData.dataItems
-                                    : DownloadsData.dataItems;
-    for (let dataItem of dataItems) {
-      if (!dataItem) {
-        continue;
-      }
-      let download = dataItem.download;
+  _activeDownloads() {
+    let downloads = this._isPrivate ? PrivateDownloadsData.downloads
+                                    : DownloadsData.downloads;
+    for (let download of downloads) {
       if (!download.stopped || (download.canceled && download.hasPartialData)) {
-        yield dataItem;
+        yield download;
       }
     }
   },
@@ -2009,7 +1707,7 @@ DownloadsIndicatorDataCtor.prototype = {
   _refreshProperties: function DID_refreshProperties()
   {
     let summary =
-      DownloadsCommon.summarizeDownloads(this._activeDataItems());
+      DownloadsCommon.summarizeDownloads(this._activeDownloads());
 
     // Determine if the indicator should be shown or get attention.
     this._hasDownloads = (this._itemCount > 0);
@@ -2070,7 +1768,7 @@ function DownloadsSummaryData(aIsPrivate, aNumToExclude) {
   // completely separated from one another.
   this._loading = false;
 
-  this._dataItems = [];
+  this._downloads = [];
 
   // Floating point value indicating the last number of seconds estimated until
   // the longest download will finish.  We need to store this value so that we
@@ -2110,9 +1808,9 @@ DownloadsSummaryData.prototype = {
     DownloadsViewPrototype.removeView.call(this, aView);
 
     if (this._views.length == 0) {
-      // Clear out our collection of DownloadDataItems. If we ever have
+      // Clear out our collection of Download objects. If we ever have
       // another view registered with us, this will get re-populated.
-      this._dataItems = [];
+      this._downloads = [];
     }
   },
 
@@ -2132,33 +1830,29 @@ DownloadsSummaryData.prototype = {
     this._dataItems = [];
   },
 
-  onDataItemAdded: function DSD_onDataItemAdded(aDataItem, aNewest)
-  {
-    if (aNewest) {
-      this._dataItems.unshift(aDataItem);
+  onDownloadAdded(download, newest) {
+    if (newest) {
+      this._downloads.unshift(download);
     } else {
-      this._dataItems.push(aDataItem);
+      this._downloads.push(download);
     }
 
     this._updateViews();
   },
 
-  onDataItemRemoved: function DSD_onDataItemRemoved(aDataItem)
-  {
-    let itemIndex = this._dataItems.indexOf(aDataItem);
-    this._dataItems.splice(itemIndex, 1);
-    this._updateViews();
-  },
-
-  // DownloadsView
-  onDataItemStateChanged() {
+  onDownloadStateChanged() {
     // Since the state of a download changed, reset the estimated time left.
     this._lastRawTimeLeft = -1;
     this._lastTimeLeft = -1;
   },
 
-  // DownloadsView
-  onDataItemChanged() {
+  onDownloadChanged() {
+    this._updateViews();
+  },
+
+  onDownloadRemoved(download) {
+    let itemIndex = this._downloads.indexOf(download);
+    this._downloads.splice(itemIndex, 1);
     this._updateViews();
   },
 
@@ -2197,17 +1891,16 @@ DownloadsSummaryData.prototype = {
   //// Property updating based on current download status
 
   /**
-   * A generator function for the dataItems that this summary is currently
+   * A generator function for the Download objects this summary is currently
    * interested in. This generator is passed off to summarizeDownloads in order
-   * to generate statistics about the dataItems we care about - in this case,
-   * it's the dataItems in this._dataItems after the first few to exclude,
+   * to generate statistics about the downloads we care about - in this case,
+   * it's the downloads in this._downloads after the first few to exclude,
    * which was set when constructing this DownloadsSummaryData instance.
    */
-  _dataItemsForSummary: function DSD_dataItemsForSummary()
-  {
-    if (this._dataItems.length > 0) {
-      for (let i = this._numToExclude; i < this._dataItems.length; ++i) {
-        yield this._dataItems[i];
+  _downloadsForSummary() {
+    if (this._downloads.length > 0) {
+      for (let i = this._numToExclude; i < this._downloads.length; ++i) {
+        yield this._downloads[i];
       }
     }
   },
@@ -2219,7 +1912,7 @@ DownloadsSummaryData.prototype = {
   {
     // Pre-load summary with default values.
     let summary =
-      DownloadsCommon.summarizeDownloads(this._dataItemsForSummary());
+      DownloadsCommon.summarizeDownloads(this._downloadsForSummary());
 
     this._description = DownloadsCommon.strings
                                        .otherDownloads2(summary.numActive);
diff --git a/application/palemoon/components/downloads/content/allDownloadsViewOverlay.js b/application/palemoon/components/downloads/content/allDownloadsViewOverlay.js
index 59da61c91..a895bd9f6 100644
--- a/application/palemoon/components/downloads/content/allDownloadsViewOverlay.js
+++ b/application/palemoon/components/downloads/content/allDownloadsViewOverlay.js
@@ -2,8 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-XPCOMUtils.defineLazyModuleGetter(this, "DownloadsDataItem",
-                                  "resource:///modules/DownloadsCommon.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "RecentWindow",
                                   "resource:///modules/RecentWindow.jsm");
 
@@ -128,21 +126,6 @@ HistoryDownload.prototype = {
 };
 
 /**
- * Represents a download from the browser history. It uses the same interface as
- * the DownloadsDataItem object.
- *
- * @param aPlacesNode
- *        The Places node for the history download.
- */
-function DownloadsHistoryDataItem(aPlacesNode) {
-  this.download = new HistoryDownload(aPlacesNode);
-}
-
-DownloadsHistoryDataItem.prototype = {
-  __proto__: DownloadsDataItem.prototype,
-};
-
-/**
  * A download element shell is responsible for handling the commands and the
  * displayed data for a single download view element.
  *
@@ -157,23 +140,23 @@ DownloadsHistoryDataItem.prototype = {
  * The caller is also responsible for forwarding status notifications for
  * session downloads, calling the onStateChanged and onChanged methods.
  *
- * @param [optional] aSessionDataItem
- *        The session download, required if aHistoryDataItem is not set.
- * @param [optional] aHistoryDataItem
- *        The history download, required if aSessionDataItem is not set.
+ * @param [optional] aSessionDownload
+ *        The session download, required if aHistoryDownload is not set.
+ * @param [optional] aHistoryDownload
+ *        The history download, required if aSessionDownload is not set.
  */
-function HistoryDownloadElementShell(aSessionDataItem, aHistoryDataItem) {
+function HistoryDownloadElementShell(aSessionDownload, aHistoryDownload) {
   this.element = document.createElement("richlistitem");
   this.element._shell = this;
 
   this.element.classList.add("download");
   this.element.classList.add("download-state");
 
-  if (aSessionDataItem) {
-    this.sessionDataItem = aSessionDataItem;
+  if (aSessionDownload) {
+    this.sessionDownload = aSessionDownload;
   }
-  if (aHistoryDataItem) {
-    this.historyDataItem = aHistoryDataItem;
+  if (aHistoryDownload) {
+    this.historyDownload = aHistoryDownload;
   }
 }
 
@@ -196,20 +179,20 @@ HistoryDownloadElementShell.prototype = {
   get active() !!this._active,
 
   /**
-   * DownloadsDataItem or DownloadsHistoryDataItem object to use for displaying
-   * information and for executing commands in the user interface.
+   * Overrides the base getter to return the Download or HistoryDownload object
+   * for displaying information and executing commands in the user interface.
    */
-  get dataItem() this._sessionDataItem || this._historyDataItem,
-
-  _sessionDataItem: null,
-  get sessionDataItem() this._sessionDataItem,
-  set sessionDataItem(aValue) {
-    if (this._sessionDataItem != aValue) {
-      if (!aValue && !this._historyDataItem) {
-        throw new Error("Should always have either a dataItem or a historyDataItem");
+  get download() this._sessionDownload || this._historyDownload,
+
+  _sessionDownload: null,
+  get sessionDownload() this._sessionDownload,
+  set sessionDownload(aValue) {
+    if (this._sessionDownload != aValue) {
+      if (!aValue && !this._historyDownload) {
+        throw new Error("Should always have either a Download or a HistoryDownload");
       }
 
-      this._sessionDataItem = aValue;
+      this._sessionDownload = aValue;
 
       this.ensureActive();
       this._updateUI();
@@ -217,19 +200,19 @@ HistoryDownloadElementShell.prototype = {
     return aValue;
   },
 
-  _historyDataItem: null,
-  get historyDataItem() this._historyDataItem,
-  set historyDataItem(aValue) {
-    if (this._historyDataItem != aValue) {
-      if (!aValue && !this._sessionDataItem) {
-        throw new Error("Should always have either a dataItem or a historyDataItem");
+  _historyDownload: null,
+  get historyDownload() this._historyDownload,
+  set historyDownload(aValue) {
+    if (this._historyDownload != aValue) {
+      if (!aValue && !this._sessionDownload) {
+        throw new Error("Should always have either a Download or a HistoryDownload");
       }
 
-      this._historyDataItem = aValue;
+      this._historyDownload = aValue;
 
       // We don't need to update the UI if we had a session data item, because
       // the places information isn't used in this case.
-      if (!this._sessionDataItem) {
+      if (!this._sessionDownload) {
         this._updateUI();
       }
     }
@@ -286,7 +269,7 @@ HistoryDownloadElementShell.prototype = {
         // We cannot open a session download file unless it's succeeded.
         // If it's succeeded, we need to make sure the file was not removed,
         // as we do for past downloads.
-        if (this._sessionDataItem && !this.download.succeeded) {
+        if (this._sessionDownload && !this.download.succeeded) {
           return false;
         }
 
@@ -299,7 +282,7 @@ HistoryDownloadElementShell.prototype = {
         return this.download.succeeded;
       case "downloadsCmd_show":
         // TODO: Bug 827010 - Handle part-file asynchronously.
-        if (this._sessionDataItem && this.download.target.partFilePath) {
+        if (this._sessionDownload && this.download.target.partFilePath) {
           let partFile = new FileUtils.File(this.download.target.partFilePath);
           if (partFile.exists()) {
             return true;
@@ -323,7 +306,7 @@ HistoryDownloadElementShell.prototype = {
         // We don't want in-progress downloads to be removed accidentally.
         return this.download.stopped;
       case "downloadsCmd_cancel":
-        return !!this._sessionDataItem;
+        return !!this._sessionDownload;
     }
     return false;
   },
@@ -351,13 +334,13 @@ HistoryDownloadElementShell.prototype = {
         break;
       }
       case "cmd_delete": {
-        if (this._sessionDataItem) {
+        if (this._sessionDownload) {
           Downloads.getList(Downloads.ALL)
                    .then(list => list.remove(this.download))
                    .then(() => this.download.finalize(true))
                    .catch(Cu.reportError);
         }
-        if (this._historyDataItem) {
+        if (this._historyDownload) {
           let uri = NetUtil.newURI(this.download.source.url);
           PlacesUtils.bhistory.removePage(uri);
         }
@@ -480,7 +463,7 @@ function DownloadsPlacesView(aRichListBox, aActive = true) {
   this._downloadElementsShellsForURI = new Map();
 
   // Map download data items to their element shells.
-  this._viewItemsForDataItems = new WeakMap();
+  this._viewItemsForDownloads = new WeakMap();
 
   // Points to the last session download element. We keep track of this
   // in order to keep all session downloads above past downloads.
@@ -626,14 +609,12 @@ DownloadsPlacesView.prototype = {
    *     alongside the other session downloads. If we don't, then we go ahead
    *     and create a new element for the download.
    *
-   * @param aDataItem
-   *        The data item of a session download. Set to null for history
-   *        downloads data.
+   * @param [optional] sessionDownload
+   *        A Download object, or null for history downloads.
    * @param [optional] aPlacesNode
-   *        The places node for a history download. Required if there's no data
-   *        item.
+   *        The Places node for a history download, or null for session downloads.
    * @param [optional] aNewest
-   *        @see onDataItemAdded. Ignored for history downloads.
+   *        @see onDownloadAdded. Ignored for history downloads.
    * @param [optional] aDocumentFragment
    *        To speed up the appending of multiple elements to the end of the
    *        list which are coming in a single batch (i.e. invalidateContainer),
@@ -641,10 +622,8 @@ DownloadsPlacesView.prototype = {
    *        be appended. It's the caller's job to ensure the fragment is merged
    *        to the richlistbox at the end.
    */
-  _addDownloadData:
-  function DPV_addDownloadData(aDataItem, aPlacesNode, aNewest = false,
+  _addDownloadData(sessionDownload, aPlacesNode, aNewest = false,
                                aDocumentFragment = null) {
-    let sessionDownload = aDataItem && aDataItem.download;
     let downloadURI = aPlacesNode ? aPlacesNode.uri
                                   : sessionDownload.source.url;
     let shellsForURI = this._downloadElementsShellsForURI.get(downloadURI);
@@ -670,21 +649,21 @@ DownloadsPlacesView.prototype = {
     //    item).
     //
     // Note: If a cancelled session download is already in the list, and the
-    // download is retired, onDataItemAdded is called again for the same
+    // download is retried, onDownloadAdded is called again for the same
     // data item. Thus, we also check that we make sure we don't have a view item
     // already.
     if (!shouldCreateShell &&
-        aDataItem && !this._viewItemsForDataItems.has(aDataItem)) {
+        sessionDownload && !this._viewItemsForDownloads.has(sessionDownload)) {
       // If there's a past-download-only shell for this download-uri with no
       // associated data item, use it for the new data item. Otherwise, go ahead
       // and create another shell.
       shouldCreateShell = true;
       for (let shell of shellsForURI) {
-        if (!shell.sessionDataItem) {
+        if (!shell.sessionDownload) {
           shouldCreateShell = false;
-          shell.sessionDataItem = aDataItem;
+          shell.sessionDownload = sessionDownload;
           newOrUpdatedShell = shell;
-          this._viewItemsForDataItems.set(aDataItem, shell);
+          this._viewItemsForDownloads.set(sessionDownload, shell);
           break;
         }
       }
@@ -694,18 +673,20 @@ DownloadsPlacesView.prototype = {
       // If we are adding a new history download here, it means there is no
       // associated session download, thus we must read the Places metadata,
       // because it will not be obscured by the session download.
-      let historyDataItem = null;
+      let historyDownload = null;
       if (aPlacesNode) {
         let metaData = this._getCachedPlacesMetaDataFor(aPlacesNode.uri);
-        historyDataItem = new DownloadsHistoryDataItem(aPlacesNode);
-        historyDataItem.download.updateFromMetaData(metaData);
+        historyDownload = new HistoryDownload(aPlacesNode);
+        historyDownload.updateFromMetaData(metaData);
       }
-      let shell = new HistoryDownloadElementShell(aDataItem, historyDataItem);
+      let shell = new HistoryDownloadElementShell(sessionDownload,
+                                                  historyDownload);
       shell.element._placesNode = aPlacesNode;
       newOrUpdatedShell = shell;
       shellsForURI.add(shell);
-      if (aDataItem)
-        this._viewItemsForDataItems.set(aDataItem, shell);
+      if (sessionDownload) {
+        this._viewItemsForDownloads.set(sessionDownload, shell);
+      }
     }
     else if (aPlacesNode) {
       // We are updating information for a history download for which we have
@@ -720,9 +701,9 @@ DownloadsPlacesView.prototype = {
       //    changed, just the reference to the Places node object is different.
       // So, we update all the node references and keep the metadata intact.
       for (let shell of shellsForURI) {
-        if (!shell.historyDataItem) {
+        if (!shell.historyDownload) {
           // Create the element to host the metadata when needed.
-          shell.historyDataItem = new DownloadsHistoryDataItem(aPlacesNode);
+          shell.historyDownload = new HistoryDownload(aPlacesNode);
         }
         shell.element._placesNode = aPlacesNode;
       }
@@ -740,7 +721,7 @@ DownloadsPlacesView.prototype = {
         // More generally, if a new download is added, should be made visible.
         this._richlistbox.ensureElementIsVisible(newOrUpdatedShell.element);
       }
-      else if (aDataItem) {
+      } else if (sessionDownload) {
         let before = this._lastSessionDownloadElement ?
           this._lastSessionDownloadElement.nextSibling : this._richlistbox.firstChild;
         this._richlistbox.insertBefore(newOrUpdatedShell.element, before);
@@ -791,8 +772,8 @@ DownloadsPlacesView.prototype = {
     let shellsForURI = this._downloadElementsShellsForURI.get(downloadURI);
     if (shellsForURI) {
       for (let shell of shellsForURI) {
-        if (shell.sessionDataItem) {
-          shell.historyDataItem = null;
+        if (shell.sessionDownload) {
+          shell.historyDownload = null;
         }
         else {
           this._removeElement(shell.element);
@@ -804,15 +785,13 @@ DownloadsPlacesView.prototype = {
     }
   },
 
-  _removeSessionDownloadFromView:
-  function DPV__removeSessionDownloadFromView(aDataItem) {
-    let download = aDataItem.download;
+  _removeSessionDownloadFromView(download) {
     let shells = this._downloadElementsShellsForURI
                      .get(download.source.url);
     if (shells.size == 0)
       throw new Error("Should have had at leaat one shell for this uri");
 
-    let shell = this._viewItemsForDataItems.get(aDataItem);
+    let shell = this._viewItemsForDownloads.get(download);
     if (!shells.has(shell))
       throw new Error("Missing download element shell in shells list for url");
 
@@ -820,7 +799,7 @@ DownloadsPlacesView.prototype = {
     // view item for this this particular data item go away.
     // If there's only one item for this download uri, we should only
     // keep it if it is associated with a history download.
-    if (shells.size > 1 || !shell.historyDataItem) {
+    if (shells.size > 1 || !shell.historyDownload) {
       this._removeElement(shell.element);
       shells.delete(shell);
       if (shells.size == 0)
@@ -832,10 +811,10 @@ DownloadsPlacesView.prototype = {
       // Previously, we did not use the Places metadata because it was obscured
       // by the session download. Since this is no longer the case, we have to
       // read the latest metadata before removing the session download.
-      let url = shell.historyDataItem.download.source.url;
+      let url = shell.historyDownload.source.url;
       let metaData = this._getPlacesMetaDataFor(url);
-      shell.historyDataItem.download.updateFromMetaData(metaData);
-      shell.sessionDataItem = null;
+      shell.historyDownload.updateFromMetaData(metaData);
+      shell.sessionDownload = null;
       // Move it below the session-download items;
       if (this._lastSessionDownloadElement == shell.element) {
         this._lastSessionDownloadElement = shell.element.previousSibling;
@@ -1108,22 +1087,20 @@ DownloadsPlacesView.prototype = {
     this._ensureInitialSelection();
   },
 
-  onDataItemAdded: function DPV_onDataItemAdded(aDataItem, aNewest) {
-    this._addDownloadData(aDataItem, null, aNewest);
+  onDownloadAdded(download, newest) {
+    this._addDownloadData(download, null, newest);
   },
 
-  onDataItemRemoved: function DPV_onDataItemRemoved(aDataItem) {
-    this._removeSessionDownloadFromView(aDataItem);
+  onDownloadStateChanged(download) {
+    this._viewItemsForDownloads.get(download).onStateChanged();
   },
 
-  // DownloadsView
-  onDataItemStateChanged(aDataItem) {
-    this._viewItemsForDataItems.get(aDataItem).onStateChanged();
+  onDownloadChanged(download) {
+    this._viewItemsForDownloads.get(download).onChanged();
   },
 
-  // DownloadsView
-  onDataItemChanged(aDataItem) {
-    this._viewItemsForDataItems.get(aDataItem).onChanged();
+  onDownloadRemoved(download) {
+    this._removeSessionDownloadFromView(download);
   },
 
   supportsCommand: function DPV_supportsCommand(aCommand) {
diff --git a/application/palemoon/components/downloads/content/downloads.js b/application/palemoon/components/downloads/content/downloads.js
index 05233e76d..9a6aa97e9 100644
--- a/application/palemoon/components/downloads/content/downloads.js
+++ b/application/palemoon/components/downloads/content/downloads.js
@@ -687,15 +687,15 @@ const DownloadsView = {
   loading: false,
 
   /**
-   * Ordered array of all DownloadsDataItem objects.  We need to keep this array
-   * because only a limited number of items are shown at once, and if an item
-   * that is currently visible is removed from the list, we might need to take
-   * another item from the array and make it appear at the bottom.
+   * Ordered array of all Download objects.  We need to keep this array because
+   * only a limited number of items are shown at once, and if an item that is
+   * currently visible is removed from the list, we might need to take another
+   * item from the array and make it appear at the bottom.
    */
-  _dataItems: [],
+  _downloads: [],
 
   /**
-   * Associates the visible DownloadsDataItem objects with their corresponding
+   * Associates the visible Download objects with their corresponding
    * DownloadsViewItem object.  There is a limited number of view items in the
    * panel at any given time.
    */
@@ -707,8 +707,8 @@ const DownloadsView = {
   _itemCountChanged: function DV_itemCountChanged()
   {
     DownloadsCommon.log("The downloads item count has changed - we are tracking",
-                        this._dataItems.length, "downloads in total.");
-    let count = this._dataItems.length;
+                        this._downloads.length, "downloads in total.");
+    let count = this._downloads.length;
     let hiddenCount = count - this.kItemCountLimit;
 
     if (count > 0) {
@@ -797,8 +797,8 @@ const DownloadsView = {
    * Called when a new download data item is available, either during the
    * asynchronous data load or when a new download is started.
    *
-   * @param aDataItem
-   *        DownloadsDataItem object that was just added.
+   * @param aDownload
+   *        Download object that was just added.
    * @param aNewest
    *        When true, indicates that this item is the most recent and should be
    *        added in the topmost position.  This happens when a new download is
@@ -806,28 +806,28 @@ const DownloadsView = {
    *        and should be appended.  The latter generally happens during the
    *        asynchronous data load.
    */
-  onDataItemAdded: function DV_onDataItemAdded(aDataItem, aNewest)
+  onDownloadAdded(download, aNewest) {
   {
     DownloadsCommon.log("A new download data item was added - aNewest =",
                         aNewest);
 
     if (aNewest) {
-      this._dataItems.unshift(aDataItem);
+      this._downloads.unshift(download);
     } else {
-      this._dataItems.push(aDataItem);
+      this._downloads.push(download);
     }
 
-    let itemsNowOverflow = this._dataItems.length > this.kItemCountLimit;
+    let itemsNowOverflow = this._downloads.length > this.kItemCountLimit;
     if (aNewest || !itemsNowOverflow) {
       // The newly added item is visible in the panel and we must add the
       // corresponding element.  This is either because it is the first item, or
       // because it was added at the bottom but the list still doesn't overflow.
-      this._addViewItem(aDataItem, aNewest);
+      this._addViewItem(download, aNewest);
     }
     if (aNewest && itemsNowOverflow) {
       // If the list overflows, remove the last item from the panel to make room
       // for the new one that we just added at the top.
-      this._removeViewItem(this._dataItems[this.kItemCountLimit]);
+      this._removeViewItem(this._downloads[this.kItemCountLimit]);
     }
 
     // For better performance during batch loads, don't update the count for
@@ -837,48 +837,45 @@ const DownloadsView = {
     }
   },
 
+  onDownloadStateChanged(download) {
+    let viewItem = this._visibleViewItems.get(download);
+    if (viewItem) {
+      viewItem.onStateChanged();
+    }
+  },
+
+  onDownloadChanged(download) {
+    let viewItem = this._visibleViewItems.get(download);
+    if (viewItem) {
+      viewItem.onChanged();
+    }
+  },
+
   /**
    * Called when a data item is removed.  Ensures that the widget associated
    * with the view item is removed from the user interface.
    *
-   * @param aDataItem
-   *        DownloadsDataItem object that is being removed.
+   * @param download
+   *        Download object that is being removed.
    */
-  onDataItemRemoved: function DV_onDataItemRemoved(aDataItem)
-  {
+  onDownloadRemoved(download) {
     DownloadsCommon.log("A download data item was removed.");
 
-    let itemIndex = this._dataItems.indexOf(aDataItem);
-    this._dataItems.splice(itemIndex, 1);
+    let itemIndex = this._downloads.indexOf(download);
+    this._downloads.splice(itemIndex, 1);
 
     if (itemIndex < this.kItemCountLimit) {
       // The item to remove is visible in the panel.
-      this._removeViewItem(aDataItem);
-      if (this._dataItems.length >= this.kItemCountLimit) {
+      this._removeViewItem(download);
+      if (this._downloads.length >= this.kItemCountLimit) {
         // Reinsert the next item into the panel.
-        this._addViewItem(this._dataItems[this.kItemCountLimit - 1], false);
+        this._addViewItem(this._downloads[this.kItemCountLimit - 1], false);
       }
     }
 
     this._itemCountChanged();
   },
 
-  // DownloadsView
-  onDataItemStateChanged(aDataItem) {
-    let viewItem = this._visibleViewItems.get(aDataItem);
-    if (viewItem) {
-      viewItem.onStateChanged();
-    }
-  },
-
-  // DownloadsView
-  onDataItemChanged(aDataItem) {
-    let viewItem = this._visibleViewItems.get(aDataItem);
-    if (viewItem) {
-      viewItem.onChanged();
-    }
-  },
-
   /**
    * Associates each richlistitem for a download with its corresponding
    * DownloadsViewItemController object.
@@ -893,15 +890,15 @@ const DownloadsView = {
    * Creates a new view item associated with the specified data item, and adds
    * it to the top or the bottom of the list.
    */
-  _addViewItem: function DV_addViewItem(aDataItem, aNewest)
+  _addViewItem(download, aNewest)
   {
     DownloadsCommon.log("Adding a new DownloadsViewItem to the downloads list.",
                         "aNewest =", aNewest);
 
     let element = document.createElement("richlistitem");
-    let viewItem = new DownloadsViewItem(aDataItem, element);
-    this._visibleViewItems.set(aDataItem, viewItem);
-    let viewItemController = new DownloadsViewItemController(aDataItem);
+    let viewItem = new DownloadsViewItem(download, element);
+    this._visibleViewItems.set(download, viewItem);
+    let viewItemController = new DownloadsViewItemController(download);
     this._controllersForElements.set(element, viewItemController);
     if (aNewest) {
       this.richListBox.insertBefore(element, this.richListBox.firstChild);
@@ -913,17 +910,17 @@ const DownloadsView = {
   /**
    * Removes the view item associated with the specified data item.
    */
-  _removeViewItem: function DV_removeViewItem(aDataItem)
+  _removeViewItem(download) {
   {
     DownloadsCommon.log("Removing a DownloadsViewItem from the downloads list.");
-    let element = this._visibleViewItems.get(aDataItem).element;
+    let element = this._visibleViewItems.get(download).element;
     let previousSelectedIndex = this.richListBox.selectedIndex;
     this.richListBox.removeChild(element);
     if (previousSelectedIndex != -1) {
       this.richListBox.selectedIndex = Math.min(previousSelectedIndex,
                                                 this.richListBox.itemCount - 1);
     }
-    this._visibleViewItems.delete(aDataItem);
+    this._visibleViewItems.delete(download);
     this._controllersForElements.delete(element);
   },
 
@@ -1053,14 +1050,13 @@ XPCOMUtils.defineConstant(this, "DownloadsView", DownloadsView);
  * Builds and updates a single item in the downloads list widget, responding to
  * changes in the download state and real-time data.
  *
- * @param aDataItem
- *        DownloadsDataItem to be associated with the view item.
+ * @param download
+ *        Download object to be associated with the view item.
  * @param aElement
  *        XUL element corresponding to the single download item in the view.
  */
-function DownloadsViewItem(aDataItem, aElement)
-{
-  this.dataItem = aDataItem;
+function DownloadsViewItem(download, aElement) {
+  this.download = download;
 
   this.element = aElement;
   this.element._shell = this;
@@ -1076,11 +1072,6 @@ DownloadsViewItem.prototype = {
   __proto__: DownloadElementShell.prototype,
 
   /**
-   * The DownloadDataItem associated with this view item.
-   */
-  dataItem: null,
-
-  /**
    * The XUL element corresponding to the associated richlistbox item.
    */
   _element: null,
@@ -1233,21 +1224,11 @@ XPCOMUtils.defineConstant(this, "DownloadsViewController", DownloadsViewControll
  * Handles all the user interaction events, in particular the "commands",
  * related to a single item in the downloads list widgets.
  */
-function DownloadsViewItemController(aDataItem) {
-  this.dataItem = aDataItem;
+function DownloadsViewItemController(download) {
+  this.download = download;
 }
 
 DownloadsViewItemController.prototype = {
-  //////////////////////////////////////////////////////////////////////////////
-  //// Command dispatching
-
-  /**
-   * The DownloadDataItem controlled by this object.
-   */
-  dataItem: null,
-
-  get download() this.dataItem.download,
-
   isCommandEnabled: function DVIC_isCommandEnabled(aCommand)
   {
     switch (aCommand) {
diff --git a/application/palemoon/components/downloads/content/downloadsViewCommon.js b/application/palemoon/components/downloads/content/downloadsViewCommon.js
index 7d18eadc6..9ef492764 100644
--- a/application/palemoon/components/downloads/content/downloadsViewCommon.js
+++ b/application/palemoon/components/downloads/content/downloadsViewCommon.js
@@ -45,7 +45,8 @@ XPCOMUtils.defineLazyModuleGetter(this, "Task",
  * from the JavaScript API for downloads, and commands are executed using a
  * combination of Download methods and DownloadsCommon.jsm helper functions.
  *
- * Specialized versions of this shell must be defined, currently they are the
+ * Specialized versions of this shell must be defined, and they are required to
+ * implement the "download" property or getter. Currently these objects are the
  * HistoryDownloadElementShell and the DownloadsViewItem for the panel. The
  * history view may use a HistoryDownload object in place of a Download object.
  */
@@ -58,17 +59,6 @@ DownloadElementShell.prototype = {
   element: null,
 
   /**
-   * The DownloadsDataItem for the download, overridden by the derived object.
-   */
-  dataItem: null,
-
-  /**
-   * Download or HistoryDownload object to use for displaying information and
-   * for executing commands in the user interface.
-   */
-  get download() this.dataItem.download,
-
-  /**
    * URI string for the file type icon displayed in the download element.
    */
   get image() {