diff -r 40f7e81126a2 content/base/src/nsGkAtomList.h
--- a/content/base/src/nsGkAtomList.h	Thu Jan 01 16:18:33 2009 -0800
+++ b/content/base/src/nsGkAtomList.h	Thu Jan 01 21:42:11 2009 -0400
@@ -406,6 +406,7 @@ GK_ATOM(headers, "headers")
 GK_ATOM(headers, "headers")
 GK_ATOM(height, "height")
 GK_ATOM(hidden, "hidden")
+GK_ATOM(hiddenfocus, "hiddenfocus")
 GK_ATOM(hidechrome, "hidechrome")
 GK_ATOM(highest, "highest")
 GK_ATOM(horizontal, "horizontal")
diff -r 40f7e81126a2 docshell/base/nsDocShell.cpp
--- a/docshell/base/nsDocShell.cpp	Thu Jan 01 16:18:33 2009 -0800
+++ b/docshell/base/nsDocShell.cpp	Thu Jan 01 21:42:11 2009 -0400
@@ -296,7 +296,6 @@ nsDocShell::nsDocShell():
     mObserveErrorPages(PR_TRUE),
     mAllowAuth(PR_TRUE),
     mAllowKeywordFixup(PR_FALSE),
-    mIsOffScreenBrowser(PR_FALSE),
     mFiredUnloadEvent(PR_FALSE),
     mEODForCurrentDocument(PR_FALSE),
     mURIResultedInDocument(PR_FALSE),
@@ -3954,8 +3953,7 @@ nsDocShell::GetVisibility(PRBool * aVisi
         return NS_OK;
 
     // otherwise, we must walk up the document and view trees checking
-    // for a hidden view, unless we're an off screen browser, which 
-    // would make this test meaningless.
+    // for a hidden view.
 
     nsCOMPtr<nsIDocShellTreeItem> treeItem = this;
     nsCOMPtr<nsIDocShellTreeItem> parentItem;
@@ -3979,9 +3977,7 @@ nsDocShell::GetVisibility(PRBool * aVisi
         NS_ASSERTION(shellContent, "subshell not in the map");
 
         nsIFrame* frame = pPresShell->GetPrimaryFrameFor(shellContent);
-        PRBool isDocShellOffScreen = PR_FALSE;
-        docShell->GetIsOffScreenBrowser(&isDocShellOffScreen);
-        if (frame && !frame->AreAncestorViewsVisible() && !isDocShellOffScreen)
+        if (frame && !frame->AreAncestorViewsVisible())
             return NS_OK;
 
         treeItem = parentItem;
@@ -3997,20 +3993,6 @@ nsDocShell::GetVisibility(PRBool * aVisi
     // Check with the tree owner as well to give embedders a chance to
     // expose visibility as well.
     return treeOwnerAsWin->GetVisibility(aVisibility);
-}
-
-NS_IMETHODIMP
-nsDocShell::SetIsOffScreenBrowser(PRBool aIsOffScreen) 
-{
-    mIsOffScreenBrowser = aIsOffScreen;
-    return NS_OK;
-}
-
-NS_IMETHODIMP
-nsDocShell::GetIsOffScreenBrowser(PRBool *aIsOffScreen) 
-{
-    *aIsOffScreen = mIsOffScreenBrowser;
-    return NS_OK;
 }
 
 NS_IMETHODIMP
diff -r 40f7e81126a2 docshell/base/nsDocShell.h
--- a/docshell/base/nsDocShell.h	Thu Jan 01 16:18:33 2009 -0800
+++ b/docshell/base/nsDocShell.h	Thu Jan 01 21:42:12 2009 -0400
@@ -575,7 +575,6 @@ protected:
     PRPackedBool               mObserveErrorPages;
     PRPackedBool               mAllowAuth;
     PRPackedBool               mAllowKeywordFixup;
-    PRPackedBool               mIsOffScreenBrowser;
 
     // This boolean is set to true right before we fire pagehide and generally
     // unset when we embed a new content viewer.  While it's true no navigation
diff -r 40f7e81126a2 docshell/base/nsIDocShell.idl
--- a/docshell/base/nsIDocShell.idl	Thu Jan 01 16:18:33 2009 -0800
+++ b/docshell/base/nsIDocShell.idl	Thu Jan 01 21:42:12 2009 -0400
@@ -68,7 +68,7 @@ interface nsISecureBrowserUI;
 interface nsISecureBrowserUI;
 interface nsIDOMStorage;
 
-[scriptable, uuid(dc4daea1-b43d-406f-bd62-c2ee879192ad)]
+[scriptable, uuid(cf974f45-d2f1-4bd5-aecd-568a1c4da454)]
 interface nsIDocShell : nsISupports
 {
   /**
@@ -466,12 +466,5 @@ interface nsIDocShell : nsISupports
    * editor data in the open document's session history entry.
    */
   [noscript, notxpcom] void DetachEditorFromWindow();
-
-  /**
-   * If true, this browser is not visible in the traditional sense, but
-   * is actively being rendered to the screen (ex. painted on a canvas)
-   * and should be treated accordingly.
-   **/
-  attribute boolean isOffScreenBrowser;    
 };
 
diff -r 40f7e81126a2 layout/generic/nsFrame.cpp
--- a/layout/generic/nsFrame.cpp	Thu Jan 01 16:18:33 2009 -0800
+++ b/layout/generic/nsFrame.cpp	Thu Jan 01 21:42:12 2009 -0400
@@ -3621,6 +3621,20 @@ nsIFrame::AreAncestorViewsVisible() cons
 {
   for (nsIView* view = GetClosestView(); view; view = view->GetParent()) {
     if (view->GetVisibility() == nsViewVisibility_kHide) {
+      // if a hidden view is associated with a deck child with the hiddenfocus
+      // attribute set to true, then we treat the view as visible.
+      nsIFrame* frame = static_cast<nsIFrame*>(view->GetClientData());
+      if (frame) {
+        nsIFrame* parentframe = frame->GetParent();
+        if (parentframe->GetType() == nsGkAtoms::deckFrame) {
+          nsIContent* content = frame->GetContent();
+          if (content && content->AttrValueIs(kNameSpaceID_None,
+                                              nsGkAtoms::hiddenfocus, nsGkAtoms::_true,
+                                              eCaseMatters))
+            continue;
+        }
+      }
+      
       return PR_FALSE;
     }
   }