--- a/mobile/android/base/java/org/mozilla/gecko/BrowserApp.java
+++ b/mobile/android/base/java/org/mozilla/gecko/BrowserApp.java
@@ -6,16 +6,17 @@
 package org.mozilla.gecko;
 
 import android.Manifest;
 import android.app.DownloadManager;
 import android.graphics.Color;
 import android.graphics.drawable.Drawable;
 import android.os.Environment;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.annotation.WorkerThread;
 import org.json.JSONArray;
 import org.mozilla.gecko.adjust.AdjustHelperInterface;
 import org.mozilla.gecko.annotation.RobocopTarget;
 import org.mozilla.gecko.AppConstants.Versions;
 import org.mozilla.gecko.DynamicToolbar.VisibilityTransition;
 import org.mozilla.gecko.Tabs.TabEvents;
 import org.mozilla.gecko.animation.PropertyAnimator;
@@ -2155,25 +2156,33 @@ public class BrowserApp extends GeckoApp
         } else {
             if (mDoorHangerPopup != null) {
                 mDoorHangerPopup.disable();
             }
             mTabsPanel.show(panel);
 
             // Hide potentially visible "find in page" bar (Bug 1177338)
             mFindInPageBar.hide();
+
+            for (final BrowserAppDelegate delegate : delegates) {
+                delegate.onTabsTrayShown(this, mTabsPanel);
+            }
         }
     }
 
     @Override
     public void hideTabs() {
         mTabsPanel.hide();
         if (mDoorHangerPopup != null) {
             mDoorHangerPopup.enable();
         }
+
+        for (final BrowserAppDelegate delegate : delegates) {
+            delegate.onTabsTrayHidden(this, mTabsPanel);
+        }
     }
 
     @Override
     public boolean autoHideTabs() {
         if (areTabsShown()) {
             hideTabs();
             return true;
         }

--- a/mobile/android/base/java/org/mozilla/gecko/BrowserAppDelegate.java
+++ b/mobile/android/base/java/org/mozilla/gecko/BrowserAppDelegate.java
@@ -2,16 +2,18 @@
  * This Source Code Form is subject to the terms of the Mozilla Public
  * 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/. */
 
 package org.mozilla.gecko;
 
 import android.os.Bundle;
 
+import org.mozilla.gecko.tabs.TabsPanel;
+
 /**
  * Abstract class for extending the behavior of BrowserApp without adding additional code to the
  * already huge class.
  */
 public abstract class BrowserAppDelegate {
     /**
      * Called when the BrowserApp activity is first created.
      */
@@ -41,9 +43,19 @@ public abstract class BrowserAppDelegate
      * Called when BrowserApp activity is no longer visible to the user.
      */
     public void onStop(BrowserApp browserApp) {}
 
     /**
      * The final call before the BrowserApp activity is destroyed.
      */
     public void onDestroy(BrowserApp browserApp) {}
+
+    /**
+     * Called when the tabs tray is opened.
+     */
+    public void onTabsTrayShown(BrowserApp browserApp, TabsPanel tabsPanel) {}
+
+    /**
+     * Called when the tabs tray is closed.
+     */
+    public void onTabsTrayHidden(BrowserApp browserApp, TabsPanel tabsPanel) {}
 }