diff --git a/xpcom/threads/nsThreadUtils.cpp b/xpcom/threads/nsThreadUtils.cpp
index 48c1ce5243c1..f29cbbafd1c7 100644
--- a/xpcom/threads/nsThreadUtils.cpp
+++ b/xpcom/threads/nsThreadUtils.cpp
@@ -41,8 +41,6 @@ static mozilla::LazyLogModule sEventDispatchAndRunLog("events");
 
 using namespace mozilla;
 
-NS_IMPL_ISUPPORTS(TailDispatchingTarget, nsIEventTarget, nsISerialEventTarget)
-
 #ifndef XPCOM_GLUE_AVOID_NSPR
 
 NS_IMPL_ISUPPORTS(IdlePeriod, nsIIdlePeriod)
diff --git a/xpcom/threads/nsThreadUtils.h b/xpcom/threads/nsThreadUtils.h
index 5f9b821d5d11..20f677556435 100644
--- a/xpcom/threads/nsThreadUtils.h
+++ b/xpcom/threads/nsThreadUtils.h
@@ -1800,56 +1800,6 @@ nsISerialEventTarget* GetCurrentSerialEventTarget();
 
 nsISerialEventTarget* GetMainThreadSerialEventTarget();
 
-// Returns a wrapper around the current thread which routes normal dispatches
-// through the tail dispatcher.
-// This means that they will run at the end of the current task, rather than
-// after all the subsequent tasks queued. This is useful to allow MozPromise
-// callbacks returned by IPDL methods to avoid an extra trip through the event
-// loop, and thus maintain correct ordering relative to other IPC events. The
-// current thread implementation must support tail dispatch.
-class TailDispatchingTarget : public nsISerialEventTarget {
- public:
-  NS_DECL_THREADSAFE_ISUPPORTS
-  TailDispatchingTarget()
-#if DEBUG
-      : mOwnerThread(AbstractThread::GetCurrent())
-#endif
-  {
-    MOZ_ASSERT(mOwnerThread, "Must be used with AbstractThreads");
-  }
-
-  NS_IMETHOD
-  Dispatch(already_AddRefed<nsIRunnable> event, uint32_t flags) override {
-    MOZ_ASSERT(flags == DISPATCH_NORMAL);
-    MOZ_ASSERT(
-        AbstractThread::GetCurrent() == mOwnerThread,
-        "TailDispatchingTarget can only be used on the thread upon which it "
-        "was created - see the comment on the class declaration.");
-    AbstractThread::DispatchDirectTask(std::move(event));
-    return NS_OK;
-  }
-  NS_IMETHOD_(bool) IsOnCurrentThreadInfallible(void) override { return true; }
-  NS_IMETHOD IsOnCurrentThread(bool* _retval) override {
-    *_retval = true;
-    return NS_OK;
-  }
-  NS_IMETHOD DispatchFromScript(nsIRunnable* event, uint32_t flags) override {
-    MOZ_ASSERT_UNREACHABLE("not implemented");
-    return NS_ERROR_NOT_IMPLEMENTED;
-  }
-  NS_IMETHOD DelayedDispatch(already_AddRefed<nsIRunnable> event,
-                             uint32_t delay) override {
-    MOZ_ASSERT_UNREACHABLE("not implemented");
-    return NS_ERROR_NOT_IMPLEMENTED;
-  }
-
- private:
-  virtual ~TailDispatchingTarget() = default;
-#if DEBUG
-  const RefPtr<AbstractThread> mOwnerThread;
-#endif
-};
-
 // Returns the number of CPUs, like PR_GetNumberOfProcessors, except
 // that it can return a cached value on platforms where sandboxing
 // would prevent reading the current value (currently Linux).  CPU