--- a/xpcom/reflect/xptinfo/xptiInterfaceInfoManager.cpp
+++ b/xpcom/reflect/xptinfo/xptiInterfaceInfoManager.cpp
@@ -76,21 +76,21 @@ XPTInterfaceInfoManager::FreeInterfaceIn
 {
     gInterfaceInfoManager = nullptr;
 }
 
 XPTInterfaceInfoManager::XPTInterfaceInfoManager()
     :   mWorkingSet(),
         mResolveLock("XPTInterfaceInfoManager.mResolveLock")
 {
-    xptiTypelibGuts* typelib = xptiTypelibGuts::Create(&XPTHeader::kHeader);
+    xptiTypelibGuts* typelib = xptiTypelibGuts::Create();
 
     ReentrantMonitorAutoEnter monitor(mWorkingSet.mTableReentrantMonitor);
-    for (uint16_t k = 0; k < XPTHeader::kHeader.mNumInterfaces; k++) {
-        VerifyAndAddEntryIfNew(XPTHeader::kHeader.mInterfaceDirectory + k, k, typelib);
+    for (uint16_t k = 0; k < XPTHeader::kNumInterfaces; k++) {
+        VerifyAndAddEntryIfNew(XPTHeader::kInterfaceDirectory + k, k, typelib);
     }
 }
 
 XPTInterfaceInfoManager::~XPTInterfaceInfoManager()
 {
     // We only do this on shutdown of the service.
     mWorkingSet.InvalidateInterfaceInfos();
 

--- a/xpcom/reflect/xptinfo/xptiTypelibGuts.cpp
+++ b/xpcom/reflect/xptinfo/xptiTypelibGuts.cpp
@@ -15,41 +15,39 @@ using namespace mozilla;
 template <class T>
 class MOZ_NEEDS_NO_VTABLE_TYPE CheckNoVTable
 {
 };
 CheckNoVTable<xptiTypelibGuts> gChecker;
 
 // static
 xptiTypelibGuts*
-xptiTypelibGuts::Create(const XPTHeader* aHeader)
+xptiTypelibGuts::Create()
 {
-    NS_ASSERTION(aHeader, "bad param");
     size_t n = sizeof(xptiTypelibGuts) +
-               sizeof(xptiInterfaceEntry*) * (aHeader->mNumInterfaces - 1);
+               sizeof(xptiInterfaceEntry*) * (XPTHeader::kNumInterfaces - 1);
     void* place = XPT_CALLOC8(gXPTIStructArena, n);
     if (!place)
         return nullptr;
-    return new(place) xptiTypelibGuts(aHeader);
+    return new(place) xptiTypelibGuts();
 }
 
 xptiInterfaceEntry*
 xptiTypelibGuts::GetEntryAt(uint16_t i)
 {
     static const nsID zeroIID =
         { 0x0, 0x0, 0x0, { 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0 } };
 
-    NS_ASSERTION(mHeader, "bad state");
     NS_ASSERTION(i < GetEntryCount(), "bad index");
 
     xptiInterfaceEntry* r = mEntryArray[i];
     if (r)
         return r;
 
-    const XPTInterfaceDirectoryEntry* iface = mHeader->mInterfaceDirectory + i;
+    const XPTInterfaceDirectoryEntry* iface = XPTHeader::kInterfaceDirectory + i;
 
     XPTInterfaceInfoManager::xptiWorkingSet& set =
         XPTInterfaceInfoManager::GetSingleton()->mWorkingSet;
 
     {
         ReentrantMonitorAutoEnter monitor(set.mTableReentrantMonitor);
         if (iface->mIID.Equals(zeroIID))
             r = set.mNameTable.Get(iface->Name());
@@ -61,15 +59,14 @@ xptiTypelibGuts::GetEntryAt(uint16_t i)
         SetEntryAt(i, r);
 
     return r;
 }
 
 const char*
 xptiTypelibGuts::GetEntryNameAt(uint16_t i)
 {
-    NS_ASSERTION(mHeader, "bad state");
     NS_ASSERTION(i < GetEntryCount(), "bad index");
 
-    const XPTInterfaceDirectoryEntry* iface = mHeader->mInterfaceDirectory + i;
+    const XPTInterfaceDirectoryEntry* iface = XPTHeader::kInterfaceDirectory + i;
 
     return iface->Name();
 }

--- a/xpcom/reflect/xptinfo/xptiprivate.h
+++ b/xpcom/reflect/xptinfo/xptiprivate.h
@@ -70,38 +70,34 @@ extern XPTArena* gXPTIStructArena;
 
 // No virtuals.
 // These are always constructed in the struct arena using placement new.
 // dtor need not be called.
 
 class xptiTypelibGuts
 {
 public:
-    static xptiTypelibGuts* Create(const XPTHeader* aHeader);
+    static xptiTypelibGuts* Create();
 
-    uint16_t GetEntryCount() const {return mHeader->mNumInterfaces;}
+    uint16_t GetEntryCount() const { return XPTHeader::kNumInterfaces; }
 
     void                SetEntryAt(uint16_t i, xptiInterfaceEntry* ptr)
     {
-        NS_ASSERTION(mHeader,"bad state!");
         NS_ASSERTION(i < GetEntryCount(),"bad param!");
         mEntryArray[i] = ptr;
     }
 
     xptiInterfaceEntry* GetEntryAt(uint16_t i);
     const char* GetEntryNameAt(uint16_t i);
 
 private:
-    explicit xptiTypelibGuts(const XPTHeader* aHeader)
-        : mHeader(aHeader)
-    { }
+    xptiTypelibGuts() = default;
     ~xptiTypelibGuts();
 
 private:
-    const XPTHeader*     mHeader;        // hold pointer into arena
     xptiInterfaceEntry*  mEntryArray[1]; // Always last. Sized to fit.
 };
 
 /***************************************************************************/
 
 /***************************************************************************/
 
 // This class exists to help xptiInterfaceInfo store a 4-state (2 bit) value

--- a/xpcom/typelib/xpt/xpt_struct.h
+++ b/xpcom/typelib/xpt/xpt_struct.h
@@ -20,20 +20,18 @@ struct XPTInterfaceDirectoryEntry;
 struct XPTInterfaceDescriptor;
 struct XPTConstDescriptor;
 struct XPTMethodDescriptor;
 struct XPTParamDescriptor;
 struct XPTTypeDescriptor;
 struct XPTTypeDescriptorPrefix;
 
 struct XPTHeader {
-  uint16_t mNumInterfaces;
-  const XPTInterfaceDirectoryEntry* mInterfaceDirectory;
-
-  static const XPTHeader kHeader;
+  static const uint16_t kNumInterfaces;
+  static const XPTInterfaceDirectoryEntry kInterfaceDirectory[];
 };
 
 /*
  * An array of directory entries is used to quickly locate an interface
  * description using its IID. No interface should appear more than once in the
  * array.
  */
 struct XPTInterfaceDirectoryEntry {