diff --git a/toolkit/components/aboutmemory/tests/test_aboutcompartments.xul b/toolkit/components/aboutmemory/tests/test_aboutcompartments.xul
index 15b0d73754ba..011196f571d9 100644
--- a/toolkit/components/aboutmemory/tests/test_aboutcompartments.xul
+++ b/toolkit/components/aboutmemory/tests/test_aboutcompartments.xul
@@ -26,6 +26,7 @@
 
   // Remove all the real reporters and multi-reporters;  save them to
   // restore at the end.
+  mgr.blockRegistration();
   var e = mgr.enumerateReporters();
   var realReporters = [];
   while (e.hasMoreElements()) {
@@ -131,10 +132,10 @@
   ];
 
   for (var i = 0; i < fakeReporters.length; i++) {
-    mgr.registerReporter(fakeReporters[i]);
+    mgr.registerReporterEvenIfBlocked(fakeReporters[i]);
   }
   for (var i = 0; i < fakeMultiReporters.length; i++) {
-    mgr.registerMultiReporter(fakeMultiReporters[i]);
+    mgr.registerMultiReporterEvenIfBlocked(fakeMultiReporters[i]);
   }
   ]]>
   </script>
@@ -193,11 +194,13 @@ Ghost Windows\n\
       mgr.unregisterMultiReporter(fakeMultiReporters[i]);
     }
     for (var i = 0; i < realReporters.length; i++) {
-      mgr.registerReporter(realReporters[i]);
+      mgr.registerReporterEvenIfBlocked(realReporters[i]);
     }
     for (var i = 0; i < realMultiReporters.length; i++) {
-      mgr.registerMultiReporter(realMultiReporters[i]);
+      mgr.registerMultiReporterEvenIfBlocked(realMultiReporters[i]);
     }
+    mgr.unblockRegistration();
+
     SimpleTest.finish();
   }
 
diff --git a/toolkit/components/aboutmemory/tests/test_aboutmemory.xul b/toolkit/components/aboutmemory/tests/test_aboutmemory.xul
index a5657049c182..d677553fc4bd 100644
--- a/toolkit/components/aboutmemory/tests/test_aboutmemory.xul
+++ b/toolkit/components/aboutmemory/tests/test_aboutmemory.xul
@@ -29,6 +29,7 @@
 
   // Remove all the real reporters and multi-reporters;  save them to
   // restore at the end.
+  mgr.blockRegistration();
   let e = mgr.enumerateReporters();
   let realReporters = [];
   while (e.hasMoreElements()) {
@@ -162,10 +163,10 @@
     }
   ];
   for (let i = 0; i < fakeReporters.length; i++) {
-    mgr.registerReporter(fakeReporters[i]);
+    mgr.registerReporterEvenIfBlocked(fakeReporters[i]);
   }
   for (let i = 0; i < fakeMultiReporters.length; i++) {
-    mgr.registerMultiReporter(fakeMultiReporters[i]);
+    mgr.registerMultiReporterEvenIfBlocked(fakeMultiReporters[i]);
   }
 
   // mgr.explicit sums "heap-allocated" and all the appropriate NONHEAP ones:
@@ -243,7 +244,7 @@
     f("5th", "explicit/b/c/i/j", NONHEAP,   5 * KB)
   ];
   for (let i = 0; i < fakeReporters2.length; i++) {
-    mgr.registerReporter(fakeReporters2[i]);
+    mgr.registerReporterEvenIfBlocked(fakeReporters2[i]);
   }
   fakeReporters = fakeReporters.concat(fakeReporters2);
   ]]>
@@ -595,11 +596,13 @@ Other Measurements\n\
       mgr.unregisterMultiReporter(fakeMultiReporters[i]);
     }
     for (let i = 0; i < realReporters.length; i++) {
-      mgr.registerReporter(realReporters[i]);
+      mgr.registerReporterEvenIfBlocked(realReporters[i]);
     }
     for (let i = 0; i < realMultiReporters.length; i++) {
-      mgr.registerMultiReporter(realMultiReporters[i]);
+      mgr.registerMultiReporterEvenIfBlocked(realMultiReporters[i]);
     }
+    mgr.unblockRegistration();
+
     SimpleTest.finish();
   }
 
diff --git a/toolkit/components/aboutmemory/tests/test_aboutmemory2.xul b/toolkit/components/aboutmemory/tests/test_aboutmemory2.xul
index 2fdb4a80da0b..7e7570068942 100644
--- a/toolkit/components/aboutmemory/tests/test_aboutmemory2.xul
+++ b/toolkit/components/aboutmemory/tests/test_aboutmemory2.xul
@@ -24,6 +24,7 @@
 
   // Remove all the real reporters and multi-reporters;  save them to
   // restore at the end.
+  mgr.blockRegistration();
   let e = mgr.enumerateReporters();
   let realReporters = [];
   while (e.hasMoreElements()) {
@@ -78,7 +79,7 @@
   ];
 
   for (let i = 0; i < fakeReporters.length; i++) {
-    mgr.registerReporter(fakeReporters[i]);
+    mgr.registerReporterEvenIfBlocked(fakeReporters[i]);
   }
 
   ]]>
@@ -97,11 +98,13 @@
       mgr.unregisterReporter(fakeReporters[i]);
     }
     for (let i = 0; i < realReporters.length; i++) {
-      mgr.registerReporter(realReporters[i]);
+      mgr.registerReporterEvenIfBlocked(realReporters[i]);
     }
     for (let i = 0; i < realMultiReporters.length; i++) {
-      mgr.registerMultiReporter(realMultiReporters[i]);
+      mgr.registerMultiReporterEvenIfBlocked(realMultiReporters[i]);
     }
+    mgr.unblockRegistration();
+
     SimpleTest.finish();
   }
 
diff --git a/toolkit/components/aboutmemory/tests/test_aboutmemory3.xul b/toolkit/components/aboutmemory/tests/test_aboutmemory3.xul
index 1cdbc8f0de73..5dcdf1094c8d 100644
--- a/toolkit/components/aboutmemory/tests/test_aboutmemory3.xul
+++ b/toolkit/components/aboutmemory/tests/test_aboutmemory3.xul
@@ -24,6 +24,7 @@
 
   // Remove all the real reporters and multi-reporters;  save them to
   // restore at the end.
+  mgr.blockRegistration();
   let e = mgr.enumerateReporters();
   let realReporters = [];
   while (e.hasMoreElements()) {
@@ -64,7 +65,7 @@
   ];
 
   for (let i = 0; i < fakeReporters.length; i++) {
-    mgr.registerReporter(fakeReporters[i]);
+    mgr.registerReporterEvenIfBlocked(fakeReporters[i]);
   }
 
   ]]>
@@ -84,11 +85,13 @@
       mgr.unregisterReporter(fakeReporters[i]);
     }
     for (let i = 0; i < realReporters.length; i++) {
-      mgr.registerReporter(realReporters[i]);
+      mgr.registerReporterEvenIfBlocked(realReporters[i]);
     }
     for (let i = 0; i < realMultiReporters.length; i++) {
-      mgr.registerMultiReporter(realMultiReporters[i]);
+      mgr.registerMultiReporterEvenIfBlocked(realMultiReporters[i]);
     }
+    mgr.unblockRegistration();
+
     SimpleTest.finish();
   }
 
diff --git a/xpcom/base/nsIMemoryReporter.idl b/xpcom/base/nsIMemoryReporter.idl
index 1e5444b024ed..c248a4fa043c 100644
--- a/xpcom/base/nsIMemoryReporter.idl
+++ b/xpcom/base/nsIMemoryReporter.idl
@@ -228,7 +228,7 @@ interface nsIMemoryMultiReporter : nsISupports
   readonly attribute int64_t explicitNonHeap;
 };
 
-[scriptable, builtinclass, uuid(0baaa958-3112-4952-b557-2a0c57eabb8f)]
+[scriptable, builtinclass, uuid(70b0e608-8dbf-4dc7-b88f-f1c745c1b48c)]
 interface nsIMemoryReporterManager : nsISupports
 {
   /*
@@ -267,6 +267,14 @@ interface nsIMemoryReporterManager : nsISupports
    */
   void unregisterMultiReporter (in nsIMemoryMultiReporter reporter);
 
+  /**
+   * These functions should only be used for testing purposes.
+   */
+  void blockRegistration();
+  void unblockRegistration();
+  void registerReporterEvenIfBlocked(in nsIMemoryReporter aReporter);
+  void registerMultiReporterEvenIfBlocked(in nsIMemoryMultiReporter aReporter);
+
   /*
    * Initialize.
    */
diff --git a/xpcom/base/nsMemoryReporterManager.cpp b/xpcom/base/nsMemoryReporterManager.cpp
index 5dc2dd6e584f..4bf20c351b45 100644
--- a/xpcom/base/nsMemoryReporterManager.cpp
+++ b/xpcom/base/nsMemoryReporterManager.cpp
@@ -822,7 +822,8 @@ HashtableEnumerator::GetNext(nsISupports** aNext)
 } // anonymous namespace
 
 nsMemoryReporterManager::nsMemoryReporterManager()
-  : mMutex("nsMemoryReporterManager::mMutex")
+  : mMutex("nsMemoryReporterManager::mMutex"),
+    mIsRegistrationBlocked(false)
 {
     mReporters.Init();
     mMultiReporters.Init();
@@ -877,13 +878,14 @@ DebugAssertRefcountIsNonZero(nsISupports* aObj)
 #endif
 }
 
-NS_IMETHODIMP
-nsMemoryReporterManager::RegisterReporter(nsIMemoryReporter *reporter)
+nsresult
+nsMemoryReporterManager::RegisterReporterHelper(
+    nsIMemoryReporter *reporter, bool aForce)
 {
     // This method is thread-safe.
     mozilla::MutexAutoLock autoLock(mMutex);
 
-    if (mReporters.Contains(reporter)) {
+    if ((mIsRegistrationBlocked && !aForce) || mReporters.Contains(reporter)) {
         return NS_ERROR_FAILURE;
     }
 
@@ -908,12 +910,27 @@ nsMemoryReporterManager::RegisterReporter(nsIMemoryReporter *reporter)
 }
 
 NS_IMETHODIMP
-nsMemoryReporterManager::RegisterMultiReporter(nsIMemoryMultiReporter *reporter)
+nsMemoryReporterManager::RegisterReporter(nsIMemoryReporter *reporter)
+{
+    return RegisterReporterHelper(reporter, /* force = */ false);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::RegisterReporterEvenIfBlocked(
+    nsIMemoryReporter *reporter)
+{
+    return RegisterReporterHelper(reporter, /* force = */ true);
+}
+
+nsresult
+nsMemoryReporterManager::RegisterMultiReporterHelper(
+    nsIMemoryMultiReporter *reporter, bool aForce)
 {
     // This method is thread-safe.
     mozilla::MutexAutoLock autoLock(mMutex);
 
-    if (mMultiReporters.Contains(reporter)) {
+    if ((mIsRegistrationBlocked && !aForce) ||
+         mMultiReporters.Contains(reporter)) {
         return NS_ERROR_FAILURE;
     }
 
@@ -927,6 +944,19 @@ nsMemoryReporterManager::RegisterMultiReporter(nsIMemoryMultiReporter *reporter)
     return NS_OK;
 }
 
+NS_IMETHODIMP
+nsMemoryReporterManager::RegisterMultiReporter(nsIMemoryMultiReporter *reporter)
+{
+    return RegisterMultiReporterHelper(reporter, /* force = */ false);
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::RegisterMultiReporterEvenIfBlocked(
+    nsIMemoryMultiReporter *reporter)
+{
+    return RegisterMultiReporterHelper(reporter, /* force = */ true);
+}
+
 NS_IMETHODIMP
 nsMemoryReporterManager::UnregisterReporter(nsIMemoryReporter *reporter)
 {
@@ -955,6 +985,30 @@ nsMemoryReporterManager::UnregisterMultiReporter(nsIMemoryMultiReporter *reporte
     return NS_OK;
 }
 
+NS_IMETHODIMP
+nsMemoryReporterManager::BlockRegistration()
+{
+    // This method is thread-safe.
+    mozilla::MutexAutoLock autoLock(mMutex);
+    if (mIsRegistrationBlocked) {
+        return NS_ERROR_FAILURE;
+    }
+    mIsRegistrationBlocked = true;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsMemoryReporterManager::UnblockRegistration()
+{
+    // This method is thread-safe.
+    mozilla::MutexAutoLock autoLock(mMutex);
+    if (!mIsRegistrationBlocked) {
+        return NS_ERROR_FAILURE;
+    }
+    mIsRegistrationBlocked = false;
+    return NS_OK;
+}
+
 NS_IMETHODIMP
 nsMemoryReporterManager::GetResident(int64_t *aResident)
 {
diff --git a/xpcom/base/nsMemoryReporterManager.h b/xpcom/base/nsMemoryReporterManager.h
index 95faae1d610f..a581b1ab8358 100644
--- a/xpcom/base/nsMemoryReporterManager.h
+++ b/xpcom/base/nsMemoryReporterManager.h
@@ -23,9 +23,14 @@ public:
   virtual ~nsMemoryReporterManager();
 
 private:
+  nsresult RegisterReporterHelper(nsIMemoryReporter *reporter, bool aForce);
+  nsresult RegisterMultiReporterHelper(nsIMemoryMultiReporter *reporter,
+                                       bool aForce);
+
   nsTHashtable<nsISupportsHashKey> mReporters;
   nsTHashtable<nsISupportsHashKey> mMultiReporters;
   Mutex mMutex;
+  bool mIsRegistrationBlocked;
 };
 
 #define NS_MEMORY_REPORTER_MANAGER_CID \