--- a/dom/base/nsWindowMemoryReporter.cpp
+++ b/dom/base/nsWindowMemoryReporter.cpp
@@ -305,16 +305,21 @@ CollectWindowReports(nsGlobalWindow *aWi
   aWindowTotalSizes->mDOMEventListenersCount +=
     windowSizes.mDOMEventListenersCount;
 
   REPORT_SIZE("/dom/other", windowSizes.mDOMOtherSize,
               "Memory used by a window's DOM that isn't measured by the "
               "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.");
   aWindowTotalSizes->mPropertyTablesSize += windowSizes.mPropertyTablesSize;
 
   REPORT_SIZE("/style-sheets", windowSizes.mStyleSheetsSize,
               "Memory used by style sheets within a window.");
   aWindowTotalSizes->mStyleSheetsSize += windowSizes.mStyleSheetsSize;
@@ -526,16 +531,19 @@ nsWindowMemoryReporter::CollectReports(n
          "This is the sum of all windows' 'dom/comment-nodes' numbers.");
 
   REPORT("window-objects/dom/event-targets", windowTotalSizes.mDOMEventTargetsSize,
          "This is the sum of all windows' 'dom/event-targets' numbers.");
 
   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.");
 
   REPORT("window-objects/style-sheets", windowTotalSizes.mStyleSheetsSize,
          "This is the sum of all windows' 'style-sheets' numbers.");
 
   REPORT("window-objects/layout/pres-shell", windowTotalSizes.mLayoutPresShellSize,

--- a/dom/base/nsWindowMemoryReporter.h
+++ b/dom/base/nsWindowMemoryReporter.h
@@ -35,16 +35,17 @@ class nsWindowSizes {
   macro(DOM,   mDOMEventTargetsSize) \
   macro(DOM,   mDOMOtherSize) \
   macro(Style, mStyleSheetsSize) \
   macro(Other, mLayoutPresShellSize) \
   macro(Style, mLayoutStyleSetsSize) \
   macro(Other, mLayoutTextRunsSize) \
   macro(Other, mLayoutPresContextSize) \
   macro(Other, mPropertyTablesSize) \
+  macro(Other, mProtoIfaceCacheSize) \
 
 public:
   nsWindowSizes(mozilla::MallocSizeOf aMallocSizeOf)
     :
       #define ZERO_SIZE(kind, mSize)  mSize(0),
       FOR_EACH_SIZE(ZERO_SIZE)
       #undef ZERO_SIZE
       mDOMEventTargetsCount(0),