diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index 4a2a96a23c7a..193a68646169 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -209,7 +209,6 @@
 #include "mozilla/dom/WindowBinding.h"
 #include "nsITabChild.h"
 #include "nsIDOMMediaQueryList.h"
-#include "mozilla/dom/DOMJSClass.h"
 
 #ifdef MOZ_WEBSPEECH
 #include "mozilla/dom/SpeechSynthesis.h"
@@ -12715,13 +12714,6 @@ nsGlobalWindow::AddSizeOfIncludingThis(nsWindowSizes* aWindowSizes) const
     const_cast<nsTHashtable<nsPtrHashKey<nsDOMEventTargetHelper> >*>
       (&mEventTargetObjects)->EnumerateEntries(CollectSizeAndListenerCount,
                                                aWindowSizes);
-
-  JSObject* global = FastGetGlobalJSObject();
-  if (IsInnerWindow() && global) {
-    ProtoAndIfaceArray* cache = GetProtoAndIfaceArray(global);
-    aWindowSizes->mProtoIfaceCacheSize +=
-      cache->SizeOfIncludingThis(aWindowSizes->mMallocSizeOf);
-  }
 }
 
 
diff --git a/dom/base/nsWindowMemoryReporter.cpp b/dom/base/nsWindowMemoryReporter.cpp
index b626a285aef9..aec88a836e91 100644
--- a/dom/base/nsWindowMemoryReporter.cpp
+++ b/dom/base/nsWindowMemoryReporter.cpp
@@ -310,11 +310,6 @@ CollectWindowReports(nsGlobalWindow *aWindow,
               "other 'dom/' numbers.");
   aWindowTotalSizes->mDOMOtherSize += windowSizes.mDOMOtherSize;
 
-  REPORT_SIZE("/proto-iface-cache", windowSizes.mProtoIfaceCacheSize,
-              "Memory used for prototype and interface binding caches "
-              "with a window.");
-  aWindowTotalSizes->mProtoIfaceCacheSize += windowSizes.mProtoIfaceCacheSize;
-
   REPORT_SIZE("/property-tables",
               windowSizes.mPropertyTablesSize,
               "Memory used for the property tables within a window.");
@@ -529,9 +524,6 @@ nsWindowMemoryReporter::CollectReports(nsIMemoryReporterCallback* aCb,
   REPORT("window-objects/dom/other", windowTotalSizes.mDOMOtherSize,
          "This is the sum of all windows' 'dom/other' numbers.");
 
-  REPORT("window-objects/proto-iface-cache", windowTotalSizes.mProtoIfaceCacheSize,
-         "This is the sum of all windows' 'proto-iface-cache' numbers.");
-
   REPORT("window-objects/property-tables",
          windowTotalSizes.mPropertyTablesSize,
          "This is the sum of all windows' 'property-tables' numbers.");
diff --git a/dom/base/nsWindowMemoryReporter.h b/dom/base/nsWindowMemoryReporter.h
index 5a7e1ab11644..1691a21402b6 100644
--- a/dom/base/nsWindowMemoryReporter.h
+++ b/dom/base/nsWindowMemoryReporter.h
@@ -40,7 +40,6 @@ class nsWindowSizes {
   macro(Other, mLayoutTextRunsSize) \
   macro(Other, mLayoutPresContextSize) \
   macro(Other, mPropertyTablesSize) \
-  macro(Other, mProtoIfaceCacheSize) \
 
 public:
   nsWindowSizes(mozilla::MallocSizeOf aMallocSizeOf)