diff --git a/widget/public/nsIWinTaskbar.idl b/widget/public/nsIWinTaskbar.idl
index 6fcf662e796d..ebebb188fd43 100644
--- a/widget/public/nsIWinTaskbar.idl
+++ b/widget/public/nsIWinTaskbar.idl
@@ -83,7 +83,7 @@ interface nsIDOMWindow;
  * See nsIJumpListBuilder for more information.
  */
 
-[scriptable, uuid(a25ad3ed-1ded-4473-bb6e-bf8b89d88949)]
+[scriptable, uuid(9fc572db-1089-4d43-9121-f4833d77a2df)]
 interface nsIWinTaskbar : nsISupports
 {
   /**
@@ -143,7 +143,7 @@ interface nsIWinTaskbar : nsISupports
    * should make use of a single instance of nsIJumpListBuilder for building lists
    * within an application.
    *
-   * @thow NS_ERROR_ALREADY_INITIALIZED if an nsIJumpListBuilder instance is
+   * @throw NS_ERROR_ALREADY_INITIALIZED if an nsIJumpListBuilder instance is
    * currently building a list.
    */
   nsIJumpListBuilder createJumpListBuilder();
@@ -167,10 +167,35 @@ interface nsIWinTaskbar : nsISupports
    * Note, when a window changes taskbar window stacks, it is placed at the
    * bottom of the new stack.
    *
-   * @thow NS_ERROR_INVALID_ARG if the window is not a valid top level window
+   * @throw NS_ERROR_INVALID_ARG if the window is not a valid top level window
    * associated with a widget.
-   * @thow NS_ERROR_FAILURE if the property on the window could not be set.
-   * @thow NS_ERROR_UNEXPECTED for general failures.
+   * @throw NS_ERROR_FAILURE if the property on the window could not be set.
+   * @throw NS_ERROR_UNEXPECTED for general failures.
    */
   void setGroupIdForWindow(in nsIDOMWindow aParent, in AString aIdentifier);
+
+  /**
+   * Notify the taskbar that a window is about to enter full screen mode.
+   *
+   * A Windows autohide taskbar will not behave correctly in all cases if
+   * it is not notified when full screen operations start and end.
+   *
+   * @throw NS_ERROR_INVALID_ARG if the window is not a valid top level window
+   * @throw NS_ERROR_UNEXPECTED for general failures.
+   * @throw NS_ERROR_NOT_AVAILABLE if the taskbar cannot be obtained.
+   */
+  void prepareFullScreen(in nsIDOMWindow aWindow, in boolean aFullScreen);
+
+  /**
+   * Notify the taskbar that a window identified by its HWND is about to enter
+   * full screen mode.
+   *
+   * A Windows autohide taskbar will not behave correctly in all cases if
+   * it is not notified when full screen operations start and end.
+   *
+   * @throw NS_ERROR_INVALID_ARG if the window is not a valid top level window
+   * @throw NS_ERROR_UNEXPECTED for general failures.
+   * @throw NS_ERROR_NOT_AVAILABLE if the taskbar cannot be obtained.
+   */
+  [noscript] void prepareFullScreenHWND(in voidPtr aWindow, in boolean aFullScreen);
 };
diff --git a/widget/src/windows/WinTaskbar.cpp b/widget/src/windows/WinTaskbar.cpp
index 2e4dc52ca9c0..24f635ef9e69 100644
--- a/widget/src/windows/WinTaskbar.cpp
+++ b/widget/src/windows/WinTaskbar.cpp
@@ -441,6 +441,37 @@ WinTaskbar::SetGroupIdForWindow(nsIDOMWindow *aParent,
   return SetWindowAppUserModelProp(aParent, nsString(aIdentifier));
 }
 
+/* void prepareFullScreen(in nsIDOMWindow aWindow, in boolean aFullScreen); */
+NS_IMETHODIMP
+WinTaskbar::PrepareFullScreen(nsIDOMWindow *aWindow, PRBool aFullScreen) {
+  NS_ENSURE_ARG_POINTER(aWindow);
+
+  HWND toplevelHWND = ::GetAncestor(GetHWNDFromDOMWindow(aWindow), GA_ROOT);
+  if (!toplevelHWND)
+    return NS_ERROR_INVALID_ARG;
+  
+  return PrepareFullScreenHWND(toplevelHWND, aFullScreen);
+}
+
+/* void prepareFullScreen(in voidPtr aWindow, in boolean aFullScreen); */
+NS_IMETHODIMP
+WinTaskbar::PrepareFullScreenHWND(void *aHWND, PRBool aFullScreen) {
+  if (!Initialize())
+    return NS_ERROR_NOT_AVAILABLE;
+
+    NS_ENSURE_ARG_POINTER(aHWND);
+
+    if (!::IsWindow((HWND)aHWND)) 
+      return NS_ERROR_INVALID_ARG;
+
+    HRESULT hr = mTaskbar->MarkFullscreenWindow((HWND)aHWND, aFullScreen);
+    if (FAILED(hr)) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    return NS_OK;
+}
+
 } // namespace widget
 } // namespace mozilla
 
diff --git a/widget/src/windows/nsWindow.cpp b/widget/src/windows/nsWindow.cpp
index b5d567505b5d..bdfad281b90f 100644
--- a/widget/src/windows/nsWindow.cpp
+++ b/widget/src/windows/nsWindow.cpp
@@ -187,9 +187,8 @@
 #endif // !defined(WINABLEAPI)
 #endif // defined(ACCESSIBILITY)
 
-#if MOZ_WINSDK_TARGETVER >= MOZ_NTDDI_WIN7
 #include "nsIWinTaskbar.h"
-#endif
+#define NS_TASKBAR_CONTRACTID "@mozilla.org/windows-taskbar;1"
 
 #if defined(NS_ENABLE_TSF)
 #include "nsTextStore.h"
@@ -2703,12 +2702,21 @@ NS_METHOD nsWindow::Invalidate(const nsIntRect & aRect, PRBool aIsSynchronous)
 NS_IMETHODIMP
 nsWindow::MakeFullScreen(PRBool aFullScreen)
 {
+  // taskbarInfo will be NULL pre Windows 7 until Bug 680227 is resolved.
+  nsCOMPtr<nsIWinTaskbar> taskbarInfo =
+    do_GetService(NS_TASKBAR_CONTRACTID);
+
   mFullscreenMode = aFullScreen;
   if (aFullScreen) {
     if (mSizeMode == nsSizeMode_Fullscreen)
       return NS_OK;
     mOldSizeMode = mSizeMode;
     SetSizeMode(nsSizeMode_Fullscreen);
+
+    // Notify the taskbar that we will be entering full screen mode.
+    if (taskbarInfo) {
+      taskbarInfo->PrepareFullScreenHWND(mWnd, TRUE);
+    }
   } else {
     SetSizeMode(mOldSizeMode);
   }
@@ -2729,6 +2737,11 @@ nsWindow::MakeFullScreen(PRBool aFullScreen)
     Invalidate(PR_FALSE);
   }
 
+  // Notify the taskbar that we have exited full screen mode.
+  if (!aFullScreen && taskbarInfo) {
+    taskbarInfo->PrepareFullScreenHWND(mWnd, FALSE);
+  }
+
   // Let the dom know via web shell window
   nsSizeModeEvent event(PR_TRUE, NS_SIZEMODE, this);
   event.mSizeMode = mSizeMode;