--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -11832,17 +11832,17 @@ nsDocument::GetVisibilityState() const
   return dom::VisibilityState::Visible;
 }
 
 /* virtual */ void
 nsDocument::PostVisibilityUpdateEvent()
 {
   nsCOMPtr<nsIRunnable> event =
     NewRunnableMethod(this, &nsDocument::UpdateVisibilityState);
-  NS_DispatchToMainThread(event);
+  Dispatch("UpdateVisibility", TaskCategory::Other, event.forget());
 }
 
 void
 nsDocument::MaybeActiveMediaComponents()
 {
   if (mEverInForeground) {
     return;
   }

--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -8661,17 +8661,17 @@ nsGlobalWindow::PostMessageMozOuter(JSCo
   JS::Rooted<JS::Value> message(aCx, aMessage);
   JS::Rooted<JS::Value> transfer(aCx, aTransfer);
 
   event->Write(aCx, message, transfer, JS::CloneDataPolicy(), aError);
   if (NS_WARN_IF(aError.Failed())) {
     return;
   }
 
-  aError = NS_DispatchToCurrentThread(event);
+  aError = Dispatch("PostMessage", TaskCategory::Other, event.forget());
 }
 
 void
 nsGlobalWindow::PostMessageMoz(JSContext* aCx, JS::Handle<JS::Value> aMessage,
                                const nsAString& aTargetOrigin,
                                JS::Handle<JS::Value> aTransfer,
                                nsIPrincipal& aSubjectPrincipal,
                                ErrorResult& aError)

--- a/dom/base/nsScriptLoader.cpp
+++ b/dom/base/nsScriptLoader.cpp
@@ -12,18 +12,19 @@
 
 #include "prsystem.h"
 #include "jsapi.h"
 #include "jsfriendapi.h"
 #include "xpcpublic.h"
 #include "nsCycleCollectionParticipant.h"
 #include "nsIContent.h"
 #include "nsJSUtils.h"
+#include "mozilla/dom/DocGroup.h"
+#include "mozilla/dom/Element.h"
 #include "mozilla/dom/ScriptSettings.h"
-#include "mozilla/dom/Element.h"
 #include "mozilla/dom/SRILogHelper.h"
 #include "nsGkAtoms.h"
 #include "nsNetUtil.h"
 #include "nsIScriptGlobalObject.h"
 #include "nsIScriptContext.h"
 #include "nsIScriptSecurityManager.h"
 #include "nsIPrincipal.h"
 #include "nsJSPrincipals.h"
@@ -1713,31 +1714,43 @@ nsScriptLoader::ProcessScriptElement(nsI
 }
 
 namespace {
 
 class NotifyOffThreadScriptLoadCompletedRunnable : public Runnable
 {
   RefPtr<nsScriptLoadRequest> mRequest;
   RefPtr<nsScriptLoader> mLoader;
+  RefPtr<DocGroup> mDocGroup;
   void *mToken;
 
 public:
   NotifyOffThreadScriptLoadCompletedRunnable(nsScriptLoadRequest* aRequest,
                                              nsScriptLoader* aLoader)
-    : mRequest(aRequest), mLoader(aLoader), mToken(nullptr)
-  {}
+    : mRequest(aRequest)
+    , mLoader(aLoader)
+    , mDocGroup(aLoader->GetDocGroup())
+    , mToken(nullptr)
+  {
+    MOZ_ASSERT(NS_IsMainThread());
+  }
 
   virtual ~NotifyOffThreadScriptLoadCompletedRunnable();
 
   void SetToken(void* aToken) {
     MOZ_ASSERT(aToken && !mToken);
     mToken = aToken;
   }
 
+  static void Dispatch(already_AddRefed<NotifyOffThreadScriptLoadCompletedRunnable>&& aSelf) {
+    RefPtr<NotifyOffThreadScriptLoadCompletedRunnable> self = aSelf;
+    RefPtr<DocGroup> docGroup = self->mDocGroup;
+    docGroup->Dispatch("OffThreadScriptLoader", TaskCategory::Other, self.forget());
+  }
+
   NS_DECL_NSIRUNNABLE
 };
 
 } /* anonymous namespace */
 
 nsresult
 nsScriptLoader::ProcessOffThreadRequest(nsScriptLoadRequest* aRequest)
 {
@@ -1805,17 +1818,17 @@ NotifyOffThreadScriptLoadCompletedRunnab
 }
 
 static void
 OffThreadScriptLoaderCallback(void *aToken, void *aCallbackData)
 {
   RefPtr<NotifyOffThreadScriptLoadCompletedRunnable> aRunnable =
     dont_AddRef(static_cast<NotifyOffThreadScriptLoadCompletedRunnable*>(aCallbackData));
   aRunnable->SetToken(aToken);
-  NS_DispatchToMainThread(aRunnable);
+  NotifyOffThreadScriptLoadCompletedRunnable::Dispatch(aRunnable.forget());
 }
 
 nsresult
 nsScriptLoader::AttemptAsyncScriptCompile(nsScriptLoadRequest* aRequest)
 {
   MOZ_ASSERT_IF(!aRequest->IsModuleRequest(), aRequest->IsReadyToRun());
   MOZ_ASSERT(!aRequest->mWasCompiledOMT);
 

--- a/dom/base/nsScriptLoader.h
+++ b/dom/base/nsScriptLoader.h
@@ -464,16 +464,21 @@ public:
    * off thread.
    */
   nsresult ProcessOffThreadRequest(nsScriptLoadRequest *aRequest);
 
   bool AddPendingChildLoader(nsScriptLoader* aChild) {
     return mPendingChildLoaders.AppendElement(aChild) != nullptr;
   }
 
+  mozilla::dom::DocGroup* GetDocGroup() const
+  {
+    return mDocument->GetDocGroup();
+  }
+
 private:
   virtual ~nsScriptLoader();
 
   nsScriptLoadRequest* CreateLoadRequest(
     nsScriptKind aKind,
     nsIScriptElement* aElement,
     uint32_t aVersion,
     mozilla::CORSMode aCORSMode,

--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -5145,17 +5145,19 @@ nsresult HTMLMediaElement::DispatchAsync
   // Save events that occur while in the bfcache. These will be dispatched
   // if the page comes out of the bfcache.
   if (mEventDeliveryPaused) {
     mPendingEvents.AppendElement(aName);
     return NS_OK;
   }
 
   nsCOMPtr<nsIRunnable> event = new nsAsyncEventRunner(aName, this);
-  NS_DispatchToMainThread(event);
+  OwnerDoc()->Dispatch("HTMLMediaElement::DispatchAsyncEvent",
+                       TaskCategory::Other,
+                       event.forget());
 
   if ((aName.EqualsLiteral("play") || aName.EqualsLiteral("playing"))) {
     mPlayTime.Start();
     if (IsHidden()) {
       HiddenVideoStart();
     }
   } else if (aName.EqualsLiteral("waiting")) {
     mPlayTime.Pause();

--- a/dom/media/mediasource/SourceBuffer.cpp
+++ b/dom/media/mediasource/SourceBuffer.cpp
@@ -352,17 +352,19 @@ SourceBuffer::DispatchSimpleEvent(const 
   DispatchTrustedEvent(NS_ConvertUTF8toUTF16(aName));
 }
 
 void
 SourceBuffer::QueueAsyncSimpleEvent(const char* aName)
 {
   MSE_DEBUG("Queuing event '%s'", aName);
   nsCOMPtr<nsIRunnable> event = new AsyncEventRunner<SourceBuffer>(this, aName);
-  NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
+  GetOwnerGlobal()->Dispatch(aName,
+                             TaskCategory::Other,
+                             event.forget());
 }
 
 void
 SourceBuffer::StartUpdating()
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(!mUpdating);
   mUpdating = true;

--- a/parser/html/nsHtml5StreamParser.cpp
+++ b/parser/html/nsHtml5StreamParser.cpp
@@ -1314,17 +1314,20 @@ nsHtml5StreamParser::FlushTreeOpsAndDisa
     // a mutex
     mFlushTimer->Cancel();
     mFlushTimerArmed = false;
   }
   if (mMode == VIEW_SOURCE_HTML || mMode == VIEW_SOURCE_XML) {
     mTokenizer->FlushViewSource();
   }
   mTreeBuilder->Flush();
-  if (NS_FAILED(NS_DispatchToMainThread(mExecutorFlusher))) {
+  nsCOMPtr<nsIRunnable> runnable(mExecutorFlusher);
+  if (NS_FAILED(mExecutor->GetDocument()->Dispatch("FlushTreeOpsAndDisarmTimer",
+                                                   dom::TaskCategory::Other,
+                                                   runnable.forget()))) {
     NS_WARNING("failed to dispatch executor flush event");
   }
 }
 
 void
 nsHtml5StreamParser::ParseAvailableData()
 {
   NS_ASSERTION(IsParserThread(), "Wrong thread!");

--- a/parser/html/nsHtml5TreeOpExecutor.cpp
+++ b/parser/html/nsHtml5TreeOpExecutor.cpp
@@ -254,17 +254,19 @@ FlushTimerCallback(nsITimer* aTimer, voi
   }
 }
 
 void
 nsHtml5TreeOpExecutor::ContinueInterruptedParsingAsync()
 {
   if (!mDocument || !mDocument->IsInBackgroundWindow()) {
     nsCOMPtr<nsIRunnable> flusher = new nsHtml5ExecutorReflusher(this);  
-    if (NS_FAILED(NS_DispatchToMainThread(flusher))) {
+    if (NS_FAILED(mDocument->Dispatch("ContinueInterruptedParsingAsync",
+                                      dom::TaskCategory::Other,
+                                      flusher.forget()))) {
       NS_WARNING("failed to dispatch executor flush event");
     }
   } else {
     if (!gBackgroundFlushList) {
       gBackgroundFlushList = new mozilla::LinkedList<nsHtml5TreeOpExecutor>();
     }
     if (!isInList()) {
       gBackgroundFlushList->insertBack(this);