--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -2891,17 +2891,17 @@ nsDocShell::SetItemType(int32_t aItemTyp
     mItemType = aItemType;
 
     // disable auth prompting for anything but content
     mAllowAuth = mItemType == typeContent; 
 
     nsRefPtr<nsPresContext> presContext = nullptr;
     GetPresContext(getter_AddRefs(presContext));
     if (presContext) {
-        presContext->InvalidateIsChromeCache();
+        presContext->UpdateIsChrome();
     }
 
     return NS_OK;
 }
 
 NS_IMETHODIMP
 nsDocShell::GetParent(nsIDocShellTreeItem ** aParent)
 {

--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -1545,17 +1545,17 @@ nsPresContext::ScreenWidthInchesForFontI
 void
 nsPresContext::SetContainer(nsIDocShell* aDocShell)
 {
   if (aDocShell) {
     mContainer = static_cast<nsDocShell*>(aDocShell)->asWeakPtr();
   } else {
     mContainer = WeakPtr<nsDocShell>();
   }
-  InvalidateIsChromeCache();
+  UpdateIsChrome();
   if (mContainer) {
     GetDocumentColorPreferences();
   }
 }
 
 nsISupports*
 nsPresContext::GetContainerWeakInternal() const
 {
@@ -2038,29 +2038,21 @@ void
 nsPresContext::CountReflows(const char * aName, nsIFrame * aFrame)
 {
   if (mShell) {
     mShell->CountReflows(aName, aFrame);
   }
 }
 #endif
 
-bool
-nsPresContext::IsChromeSlow() const
+void
+nsPresContext::UpdateIsChrome()
 {
   mIsChrome = mContainer &&
               nsIDocShellTreeItem::typeChrome == mContainer->ItemType();
-  mIsChromeIsCached = true;
-  return mIsChrome;
-}
-
-void
-nsPresContext::InvalidateIsChromeCacheExternal()
-{
-  InvalidateIsChromeCacheInternal();
 }
 
 /* virtual */ bool
 nsPresContext::HasAuthorSpecifiedRules(nsIFrame *aFrame, uint32_t ruleTypeMask) const
 {
   return
     nsRuleNode::HasAuthorSpecifiedRules(aFrame->StyleContext(),
                                         ruleTypeMask,

--- a/layout/base/nsPresContext.h
+++ b/layout/base/nsPresContext.h
@@ -808,30 +808,18 @@ public:
   gfxTextPerfMetrics *GetTextPerfMetrics() { return mTextPerf; }
 
   bool IsDynamic() { return (mType == eContext_PageLayout || mType == eContext_Galley); }
   bool IsScreen() { return (mMedium == nsGkAtoms::screen ||
                               mType == eContext_PageLayout ||
                               mType == eContext_PrintPreview); }
 
   // Is this presentation in a chrome docshell?
-  bool IsChrome() const
-  {
-    return mIsChromeIsCached ? mIsChrome : IsChromeSlow();
-  }
-
-  virtual void InvalidateIsChromeCacheExternal();
-  void InvalidateIsChromeCacheInternal() { mIsChromeIsCached = false; }
-#ifdef MOZILLA_INTERNAL_API
-  void InvalidateIsChromeCache()
-  { InvalidateIsChromeCacheInternal(); }
-#else
-  void InvalidateIsChromeCache()
-  { InvalidateIsChromeCacheExternal(); }
-#endif
+  bool IsChrome() const { return mIsChrome; }
+  void UpdateIsChrome();
 
   // Public API for native theme code to get style internals.
   virtual bool HasAuthorSpecifiedRules(nsIFrame *aFrame, uint32_t ruleTypeMask) const;
 
   // Is it OK to let the page specify colors and backgrounds?
   bool UseDocumentColors() const {
     return GetCachedBoolPref(kPresContext_UseDocumentColors) || IsChrome();
   }
@@ -1309,21 +1297,17 @@ protected:
 
   unsigned              mIsVisual : 1;
 
   unsigned              mProcessingRestyles : 1;
   unsigned              mProcessingAnimationStyleChange : 1;
 
   unsigned              mFireAfterPaintEvents : 1;
 
-  // Cache whether we are chrome or not because it is expensive.  
-  // mIsChromeIsCached tells us if mIsChrome is valid or we need to get the
-  // value the slow way.
-  mutable unsigned      mIsChromeIsCached : 1;
-  mutable unsigned      mIsChrome : 1;
+  unsigned              mIsChrome : 1;
 
   // Should we paint flash in this context? Do not use this variable directly.
   // Use GetPaintFlashing() method instead.
   mutable unsigned mPaintFlashing : 1;
   mutable unsigned mPaintFlashingInitialized : 1;
 
 #ifdef DEBUG
   bool                  mInitialized;