--- a/mobile/android/base/java/org/mozilla/gecko/BrowserApp.java
+++ b/mobile/android/base/java/org/mozilla/gecko/BrowserApp.java
@@ -303,17 +303,17 @@ public class BrowserApp extends GeckoApp
             view = TabsPanel.createTabsLayout(context, attrs);
         } else {
             view = super.onCreateView(name, context, attrs);
         }
         return view;
     }
 
     @Override
-    public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
+    public void onTabChanged(Tab tab, TabEvents msg, String data) {
         if (tab == null) {
             // Only RESTORED is allowed a null tab: it's the only event that
             // isn't tied to a specific tab.
             if (msg != Tabs.TabEvents.RESTORED) {
                 throw new IllegalArgumentException("onTabChanged:" + msg + " must specify a tab.");
             }
             return;
         }

--- a/mobile/android/base/java/org/mozilla/gecko/DoorHangerPopup.java
+++ b/mobile/android/base/java/org/mozilla/gecko/DoorHangerPopup.java
@@ -142,17 +142,17 @@ public class DoorHangerPopup extends Anc
             config.setButton(buttonJSON.getString("label"), buttonJSON.getInt("callback"), isPositive);
         }
 
         return config;
     }
 
     // This callback is automatically executed on the UI thread.
     @Override
-    public void onTabChanged(final Tab tab, final Tabs.TabEvents msg, final Object data) {
+    public void onTabChanged(final Tab tab, final Tabs.TabEvents msg, final String data) {
         switch(msg) {
             case CLOSED:
                 // Remove any doorhangers for a tab when it's closed (make
                 // a temporary set to avoid a ConcurrentModificationException)
                 removeTabDoorHangers(tab.getId(), true);
                 break;
 
             case LOCATION_CHANGE:

--- a/mobile/android/base/java/org/mozilla/gecko/FilePickerResultHandler.java
+++ b/mobile/android/base/java/org/mozilla/gecko/FilePickerResultHandler.java
@@ -251,17 +251,17 @@ class FilePickerResultHandler implements
 
         @Override
         public void onLoaderReset(Loader<Cursor> loader) { }
 
         /*Tabs.OnTabsChangedListener*/
         // This cleans up our temp file. If it doesn't run, we just hope that Android
         // will eventually does the cleanup for us.
         @Override
-        public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
+        public void onTabChanged(Tab tab, Tabs.TabEvents msg, String data) {
             if ((tab == null) || (tab.getId() != tabId)) {
                 return;
             }
 
             if (msg == Tabs.TabEvents.LOCATION_CHANGE ||
                 msg == Tabs.TabEvents.CLOSED) {
                 ThreadUtils.postToBackgroundThread(new Runnable() {
                     @Override

--- a/mobile/android/base/java/org/mozilla/gecko/GeckoApp.java
+++ b/mobile/android/base/java/org/mozilla/gecko/GeckoApp.java
@@ -268,17 +268,17 @@ public abstract class GeckoApp
     }
 
     @Override
     public FormAssistPopup getFormAssistPopup() {
         return mFormAssistPopup;
     }
 
     @Override
-    public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
+    public void onTabChanged(Tab tab, Tabs.TabEvents msg, String data) {
         // When a tab is closed, it is always unselected first.
         // When a tab is unselected, another tab is always selected first.
         switch(msg) {
             case UNSELECTED:
                 hidePlugins(tab);
                 break;
 
             case LOCATION_CHANGE:

--- a/mobile/android/base/java/org/mozilla/gecko/Tabs.java
+++ b/mobile/android/base/java/org/mozilla/gecko/Tabs.java
@@ -576,17 +576,17 @@ public class Tabs implements GeckoEventL
                         tab.loadThumbnailFromDB(db);
                     }
                 }
             }
         });
     }
 
     public interface OnTabsChangedListener {
-        public void onTabChanged(Tab tab, TabEvents msg, Object data);
+        public void onTabChanged(Tab tab, TabEvents msg, String data);
     }
 
     private static final List<OnTabsChangedListener> TABS_CHANGED_LISTENERS = new CopyOnWriteArrayList<OnTabsChangedListener>();
 
     public static void registerOnTabsChangedListener(OnTabsChangedListener listener) {
         TABS_CHANGED_LISTENERS.add(listener);
     }
 
@@ -619,17 +619,17 @@ public class Tabs implements GeckoEventL
         BOOKMARK_REMOVED,
         AUDIO_PLAYING_CHANGE,
     }
 
     public void notifyListeners(Tab tab, TabEvents msg) {
         notifyListeners(tab, msg, "");
     }
 
-    public void notifyListeners(final Tab tab, final TabEvents msg, final Object data) {
+    public void notifyListeners(final Tab tab, final TabEvents msg, final String data) {
         if (tab == null &&
             msg != TabEvents.RESTORED) {
             throw new IllegalArgumentException("onTabChanged:" + msg + " must specify a tab.");
         }
 
         ThreadUtils.postToUiThread(new Runnable() {
             @Override
             public void run() {

--- a/mobile/android/base/java/org/mozilla/gecko/gfx/BitmapUtils.java
+++ b/mobile/android/base/java/org/mozilla/gecko/gfx/BitmapUtils.java
@@ -148,17 +148,17 @@ public final class BitmapUtils {
     }
 
     public static void getThumbnailDrawable(final Context context, final String data, final BitmapLoader loader) {
          int id = Integer.parseInt(data.substring(10), 10);
          final Tab tab = Tabs.getInstance().getTab(id);
          runOnBitmapFoundOnUiThread(loader, tab.getThumbnail());
          Tabs.registerOnTabsChangedListener(new Tabs.OnTabsChangedListener() {
                  @Override
-                 public void onTabChanged(Tab t, Tabs.TabEvents msg, Object data) {
+                 public void onTabChanged(Tab t, Tabs.TabEvents msg, String data) {
                      if (tab == t && msg == Tabs.TabEvents.THUMBNAIL) {
                          Tabs.unregisterOnTabsChangedListener(this);
                          runOnBitmapFoundOnUiThread(loader, t.getThumbnail());
                      }
                  }
              });
          ThumbnailHelper.getInstance().getAndProcessThumbnailFor(tab);
     }

--- a/mobile/android/base/java/org/mozilla/gecko/gfx/LayerRenderer.java
+++ b/mobile/android/base/java/org/mozilla/gecko/gfx/LayerRenderer.java
@@ -650,17 +650,17 @@ public class LayerRenderer implements Ta
                 });
                 mView.setPaintState(LayerView.PAINT_AFTER_FIRST);
             }
             mLastFrameTime = mFrameStartTime;
         }
     }
 
     @Override
-    public void onTabChanged(final Tab tab, Tabs.TabEvents msg, Object data) {
+    public void onTabChanged(final Tab tab, Tabs.TabEvents msg, String data) {
         // Sets the background of the newly selected tab. This background color
         // gets cleared in endDrawing(). This function runs on the UI thread,
         // but other code that touches the paint state is run on the compositor
         // thread, so this may need to be changed if any problems appear.
         if (msg == Tabs.TabEvents.SELECTED) {
             if (mView != null) {
                 mView.setSurfaceBackgroundColor(tab.getBackgroundColor());
                 mView.setPaintState(LayerView.PAINT_START);

--- a/mobile/android/base/java/org/mozilla/gecko/gfx/LayerView.java
+++ b/mobile/android/base/java/org/mozilla/gecko/gfx/LayerView.java
@@ -697,17 +697,17 @@ public class LayerView extends ScrollVie
         }
     }
 
     public float getSurfaceTranslation() {
         return mSurfaceTranslation;
     }
 
     @Override
-    public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
+    public void onTabChanged(Tab tab, Tabs.TabEvents msg, String data) {
         if (msg == Tabs.TabEvents.VIEWPORT_CHANGE && Tabs.getInstance().isSelectedTab(tab) && mLayerClient != null) {
             setZoomConstraints(tab.getZoomConstraints());
             setIsRTL(tab.getIsRTL());
         }
     }
 
     // Public hooks for dynamic toolbar translation
 

--- a/mobile/android/base/java/org/mozilla/gecko/gfx/TouchEventHandler.java
+++ b/mobile/android/base/java/org/mozilla/gecko/gfx/TouchEventHandler.java
@@ -294,14 +294,14 @@ final class TouchEventHandler implements
             }
             mProcessingBalance++;
         }
     }
 
     // Tabs.OnTabsChangedListener implementation
 
     @Override
-    public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
+    public void onTabChanged(Tab tab, Tabs.TabEvents msg, String data) {
         if ((Tabs.getInstance().isSelectedTab(tab) && msg == Tabs.TabEvents.STOP) || msg == Tabs.TabEvents.SELECTED) {
             mWaitForTouchListeners = tab.getHasTouchListeners();
         }
     }
 }

--- a/mobile/android/base/java/org/mozilla/gecko/home/TwoLinePageRow.java
+++ b/mobile/android/base/java/org/mozilla/gecko/home/TwoLinePageRow.java
@@ -129,17 +129,17 @@ public class TwoLinePageRow extends Line
     }
 
     /**
      * Update the row in response to a tab change event.
      * <p>
      * This method is always invoked on the UI thread.
      */
     @Override
-    public void onTabChanged(final Tab tab, final Tabs.TabEvents msg, final Object data) {
+    public void onTabChanged(final Tab tab, final Tabs.TabEvents msg, final String data) {
         // Carefully check if this tab event is relevant to this row.
         final String pageUrl = mPageUrl;
         if (pageUrl == null) {
             return;
         }
         if (tab == null) {
             return;
         }

--- a/mobile/android/base/java/org/mozilla/gecko/prompts/Prompt.java
+++ b/mobile/android/base/java/org/mozilla/gecko/prompts/Prompt.java
@@ -128,17 +128,17 @@ public class Prompt implements OnClickLi
                 mDialog.show();
             }
         } else {
             mDialog.show();
         }
     }
 
     @Override
-    public void onTabChanged(final Tab tab, final Tabs.TabEvents msg, final Object data) {
+    public void onTabChanged(final Tab tab, final Tabs.TabEvents msg, final String data) {
         if (tab != Tabs.getInstance().getTab(mTabId)) {
             return;
         }
 
         switch(msg) {
             case SELECTED:
                 Log.i(LOGTAG, "Selected");
                 mDialog.show();

--- a/mobile/android/base/java/org/mozilla/gecko/tabs/TabStrip.java
+++ b/mobile/android/base/java/org/mozilla/gecko/tabs/TabStrip.java
@@ -102,17 +102,17 @@ public class TabStrip extends ThemedLine
     }
 
     public void setOnTabChangedListener(OnTabAddedOrRemovedListener listener) {
         tabChangedListener = listener;
     }
 
     private class TabsListener implements Tabs.OnTabsChangedListener {
         @Override
-        public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
+        public void onTabChanged(Tab tab, Tabs.TabEvents msg, String data) {
             switch (msg) {
                 case RESTORED:
                     tabStripView.restoreTabs();
                     break;
 
                 case ADDED:
                     tabStripView.addTab(tab);
                     if (tabChangedListener != null) {

--- a/mobile/android/base/java/org/mozilla/gecko/tabs/TabsGridLayout.java
+++ b/mobile/android/base/java/org/mozilla/gecko/tabs/TabsGridLayout.java
@@ -197,17 +197,17 @@ class TabsGridLayout extends GridView
         return true;
     }
 
     private void autoHidePanel() {
         tabsPanel.autoHidePanel();
     }
 
     @Override
-    public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
+    public void onTabChanged(Tab tab, Tabs.TabEvents msg, String data) {
         switch (msg) {
             case ADDED:
                 // Refresh only if panel is shown. show() will call refreshTabsData() later again.
                 if (tabsPanel.isShown()) {
                     // Refresh the list to make sure the new tab is added in the right position.
                     refreshTabsData();
                 }
                 break;

--- a/mobile/android/base/java/org/mozilla/gecko/tabs/TabsListLayout.java
+++ b/mobile/android/base/java/org/mozilla/gecko/tabs/TabsListLayout.java
@@ -103,17 +103,17 @@ class TabsListLayout extends TwoWayView
         return isVertical();
     }
 
     private void autoHidePanel() {
         tabsPanel.autoHidePanel();
     }
 
     @Override
-    public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
+    public void onTabChanged(Tab tab, Tabs.TabEvents msg, String data) {
         switch (msg) {
             case ADDED:
                 // Refresh the list to make sure the new tab is added in the right position.
                 refreshTabsData();
                 break;
 
             case CLOSED:
                 if (tab.isPrivate() == isPrivate && tabsAdapter.getCount() > 0) {

--- a/mobile/android/base/java/org/mozilla/gecko/toolbar/BrowserToolbar.java
+++ b/mobile/android/base/java/org/mozilla/gecko/toolbar/BrowserToolbar.java
@@ -398,17 +398,17 @@ public abstract class BrowserToolbar ext
         if (!isEditing()) {
             throw new IllegalStateException("Expected to be editing");
         }
 
         urlEditLayout.restoreTabEditingState(editingState);
     }
 
     @Override
-    public void onTabChanged(@NonNull Tab tab, Tabs.TabEvents msg, Object data) {
+    public void onTabChanged(@NonNull Tab tab, Tabs.TabEvents msg, String data) {
         Log.d(LOGTAG, "onTabChanged: " + msg);
         final Tabs tabs = Tabs.getInstance();
 
         // These conditions are split into three phases:
         // * Always do first
         // * Handling specific to the selected tab
         // * Always do afterwards.
 

--- a/mobile/android/tests/browser/robocop/src/org/mozilla/gecko/tests/testAccessibleCarets.java
+++ b/mobile/android/tests/browser/robocop/src/org/mozilla/gecko/tests/testAccessibleCarets.java
@@ -52,17 +52,17 @@ public class testAccessibleCarets extend
         super.testJavascript();
     }
 
     /**
      * Observes tab change events to broadcast to the test script.
      */
     private class TabsListener implements Tabs.OnTabsChangedListener {
         @Override
-        public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
+        public void onTabChanged(Tab tab, Tabs.TabEvents msg, String data) {
             switch (msg) {
                 case STOP:
                     final JSONObject args = new JSONObject();
                     try {
                         args.put("tabId", tab.getId());
                         args.put("event", msg.toString());
                     } catch (JSONException e) {
                         Log.e(LOGTAG, "Error building JSON arguments for " + TAB_CHANGE_EVENT, e);