diff --git a/docshell/base/nsDocShell.cpp b/docshell/base/nsDocShell.cpp
index b874b4bd88d..87c1414af53 100644
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -2415,6 +2415,12 @@ nsDocShell::SetItemType(PRInt32 aItemType)
     // disable auth prompting for anything but content
     mAllowAuth = mItemType == typeContent; 
 
+    nsRefPtr<nsPresContext> presContext = nsnull;
+    GetPresContext(getter_AddRefs(presContext));
+    if (presContext) {
+        presContext->UpdateIsChromeCache();
+    }
+
     return NS_OK;
 }
 
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index 360aebd2901..ee247d89901 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -1335,6 +1335,7 @@ nsPresContext::SetContainer(nsISupports* aHandler)
   if (mContainer) {
     GetDocumentColorPreferences();
   }
+  UpdateIsChromeCacheInternal();
 }
 
 already_AddRefed<nsISupports>
@@ -1624,8 +1625,8 @@ nsPresContext::CountReflows(const char * aName, nsIFrame * aFrame)
 }
 #endif
 
-PRBool
-nsPresContext::IsChrome() const
+void
+nsPresContext::UpdateIsChromeCacheInternal()
 {
   PRBool isChrome = PR_FALSE;
   nsCOMPtr<nsISupports> container = GetContainer();
@@ -1640,7 +1641,13 @@ nsPresContext::IsChrome() const
       }
     }
   }
-  return isChrome;
+  mIsChrome = isChrome;
+}
+
+void
+nsPresContext::UpdateIsChromeCacheExternal()
+{
+  UpdateIsChromeCacheInternal();
 }
 
 /* virtual */ PRBool
diff --git a/layout/base/nsPresContext.h b/layout/base/nsPresContext.h
index 845c7c502dc..2dddfa18756 100644
--- a/layout/base/nsPresContext.h
+++ b/layout/base/nsPresContext.h
@@ -810,7 +810,17 @@ public:
                               mType == eContext_PrintPreview); }
 
   // Is this presentation in a chrome docshell?
-  PRBool IsChrome() const;
+  PRBool IsChrome() const { return mIsChrome; }
+
+  virtual void UpdateIsChromeCacheExternal();
+  void UpdateIsChromeCacheInternal();
+#ifdef _IMPL_NS_LAYOUT
+  void UpdateIsChromeCache()
+  { UpdateIsChromeCacheInternal(); }
+#else
+  void UpdateIsChromeCache()
+  { UpdateIsChromeCacheExternal(); }
+#endif
 
   // Public API for native theme code to get style internals.
   virtual PRBool HasAuthorSpecifiedRules(nsIFrame *aFrame, PRUint32 ruleTypeMask) const;
@@ -1115,6 +1125,9 @@ protected:
   unsigned              mProcessingRestyles : 1;
   unsigned              mProcessingAnimationStyleChange : 1;
 
+  // Cache whether we are chrome or not because it is expensive.  
+  unsigned              mIsChrome : 1;
+
 #ifdef DEBUG
   PRBool                mInitialized;
 #endif