--- a/mobile/android/base/java/org/mozilla/gecko/GeckoApp.java
+++ b/mobile/android/base/java/org/mozilla/gecko/GeckoApp.java
@@ -1062,18 +1062,16 @@ public abstract class GeckoApp extends G
             }
         } else if (savedInstanceState != null) {
             // Bug 896992 - This intent has already been handled; reset the intent.
             setIntent(new Intent(Intent.ACTION_MAIN));
         }
 
         super.onCreate(savedInstanceState);
 
-        GeckoScreenOrientation.getInstance().update(getResources().getConfiguration().orientation);
-
         setContentView(getLayout());
 
         // Set up Gecko layout.
         mRootLayout = (RelativeLayout) findViewById(R.id.root_layout);
         mGeckoLayout = (RelativeLayout) findViewById(R.id.gecko_layout);
         mMainLayout = (RelativeLayout) findViewById(R.id.main_layout);
         mLayerView = (GeckoView) findViewById(R.id.layer_view);
 
@@ -2172,21 +2170,16 @@ public abstract class GeckoApp extends G
         Log.d(LOGTAG, "onConfigurationChanged: " + newConfig.locale);
 
         final LocaleManager localeManager = BrowserLocaleManager.getInstance();
         final Locale changed = localeManager.onSystemConfigurationChanged(this, getResources(), newConfig, mLastLocale);
         if (changed != null) {
             onLocaleChanged(Locales.getLanguageTag(changed));
         }
 
-        // onConfigurationChanged is not called for 180 degree orientation changes,
-        // we will miss such rotations and the screen orientation will not be
-        // updated.
-        GeckoScreenOrientation.getInstance().update(newConfig.orientation);
-
         if (mPromptService != null) {
             mPromptService.changePromptOrientation(newConfig.orientation);
         }
 
         super.onConfigurationChanged(newConfig);
     }
 
     public String getContentProcessName() {

--- a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/GeckoScreenOrientation.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/GeckoScreenOrientation.java
@@ -149,17 +149,17 @@ public class GeckoScreenOrientation {
     /*
      * Update screen orientation given the screen orientation.
      *
      * @param aScreenOrientation
      *        Gecko screen orientation based on android orientation and rotation.
      *
      * @return Whether the screen orientation has changed.
      */
-    public boolean update(ScreenOrientation aScreenOrientation) {
+    public synchronized boolean update(ScreenOrientation aScreenOrientation) {
         if (mScreenOrientation == aScreenOrientation) {
             return false;
         }
         mScreenOrientation = aScreenOrientation;
         Log.d(LOGTAG, "updating to new orientation " + mScreenOrientation);
         notifyListeners(mScreenOrientation);
         if (mShouldNotify) {
             // Gecko expects a definite screen orientation, so we default to the
@@ -231,38 +231,42 @@ public class GeckoScreenOrientation {
      *        rotation.
      *
      * @return Whether the locking was successful.
      */
     public boolean lock(ScreenOrientation aScreenOrientation) {
         Log.d(LOGTAG, "locking to " + aScreenOrientation);
         final ScreenOrientationDelegate delegate = GeckoAppShell.getScreenOrientationDelegate();
         final int activityInfoOrientation = screenOrientationToActivityInfoOrientation(aScreenOrientation);
-        if (delegate.setRequestedOrientationForCurrentActivity(activityInfoOrientation)) {
-            update(aScreenOrientation);
-            return true;
-        } else {
-            return false;
+        synchronized (this) {
+            if (delegate.setRequestedOrientationForCurrentActivity(activityInfoOrientation)) {
+                update(aScreenOrientation);
+                return true;
+            } else {
+                return false;
+            }
         }
     }
 
     /**
      * Unlock and update screen orientation.
      *
      * @return Whether the unlocking was successful.
      */
     public boolean unlock() {
         Log.d(LOGTAG, "unlocking");
         final ScreenOrientationDelegate delegate = GeckoAppShell.getScreenOrientationDelegate();
         final int activityInfoOrientation = screenOrientationToActivityInfoOrientation(ScreenOrientation.DEFAULT);
-        if (delegate.setRequestedOrientationForCurrentActivity(activityInfoOrientation)) {
-            update();
-            return true;
-        } else {
-            return false;
+        synchronized (this) {
+            if (delegate.setRequestedOrientationForCurrentActivity(activityInfoOrientation)) {
+                update();
+                return true;
+            } else {
+                return false;
+            }
         }
     }
 
     /*
      * Combine the Android orientation and rotation to the Gecko orientation.
      *
      * @param aAndroidOrientation
      *        Android orientation from Configuration.orientation.

--- a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoRuntime.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoRuntime.java
@@ -10,16 +10,17 @@ import android.os.Parcel;
 import android.os.Parcelable;
 import android.content.Context;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.util.Log;
 
 import org.mozilla.gecko.EventDispatcher;
 import org.mozilla.gecko.GeckoAppShell;
+import org.mozilla.gecko.GeckoScreenOrientation;
 import org.mozilla.gecko.GeckoThread;
 import org.mozilla.gecko.PrefsHelper;
 import org.mozilla.gecko.util.BundleEventListener;
 import org.mozilla.gecko.util.EventCallback;
 import org.mozilla.gecko.util.GeckoBundle;
 import org.mozilla.gecko.util.ThreadUtils;
 
 import java.io.File;
@@ -249,16 +250,32 @@ public final class GeckoRuntime implemen
      * internal data.
      *
      * @return Profile directory
      */
     @NonNull public File getProfileDir() {
         return GeckoThread.getActiveProfile().getDir();
     }
 
+    /**
+     * Notify Gecko that the screen orientation has changed.
+     */
+    public void orientationChanged() {
+        GeckoScreenOrientation.getInstance().update();
+    }
+
+    /**
+     * Notify Gecko that the screen orientation has changed.
+     * @param newOrientation The new screen orientation, as retrieved e.g. from the current
+     *                       {@link android.content.res.Configuration}.
+     */
+    public void orientationChanged(int newOrientation) {
+        GeckoScreenOrientation.getInstance().update(newOrientation);
+    }
+
     @Override // Parcelable
     public int describeContents() {
         return 0;
     }
 
     @Override // Parcelable
     public void writeToParcel(Parcel out, int flags) {
         out.writeParcelable(mSettings, flags);

--- a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoView.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoView.java
@@ -11,16 +11,17 @@ import org.mozilla.gecko.EventDispatcher
 import org.mozilla.gecko.gfx.DynamicToolbarAnimator;
 import org.mozilla.gecko.gfx.PanZoomController;
 import org.mozilla.gecko.gfx.GeckoDisplay;
 import org.mozilla.gecko.InputMethods;
 import org.mozilla.gecko.util.ActivityUtils;
 
 import android.app.Activity;
 import android.content.Context;
+import android.content.res.Configuration;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Rect;
 import android.graphics.Region;
 import android.os.Build;
 import android.os.Handler;
 import android.os.Parcel;
 import android.os.Parcelable;
@@ -336,16 +337,17 @@ public class GeckoView extends FrameLayo
     public void onAttachedToWindow() {
         if (mSession == null) {
             setSession(new GeckoSession(), GeckoRuntime.getDefault(getContext()));
         }
 
         if (!mSession.isOpen()) {
             mSession.open(mRuntime);
         }
+        mRuntime.orientationChanged();
 
         super.onAttachedToWindow();
     }
 
     @Override
     public void onDetachedFromWindow() {
         super.onDetachedFromWindow();
 
@@ -355,16 +357,28 @@ public class GeckoView extends FrameLayo
 
         // If we saved state earlier, we don't want to close the window.
         if (!mStateSaved && mSession.isOpen()) {
             mSession.close();
         }
     }
 
     @Override
+    protected void onConfigurationChanged(Configuration newConfig) {
+        super.onConfigurationChanged(newConfig);
+
+        if (mRuntime != null) {
+            // onConfigurationChanged is not called for 180 degree orientation changes,
+            // we will miss such rotations and the screen orientation will not be
+            // updated.
+            mRuntime.orientationChanged(newConfig.orientation);
+        }
+    }
+
+    @Override
     public boolean gatherTransparentRegion(final Region region) {
         // For detecting changes in SurfaceView layout, we take a shortcut here and
         // override gatherTransparentRegion, instead of registering a layout listener,
         // which is more expensive.
         if (mSurfaceView != null) {
             mDisplay.onGlobalLayout();
         }
         return super.gatherTransparentRegion(region);