diff --git a/dom/media/ipc/RDDProcessManager.cpp b/dom/media/ipc/RDDProcessManager.cpp
index 89dc004471f5..35cebbaaa72b 100644
--- a/dom/media/ipc/RDDProcessManager.cpp
+++ b/dom/media/ipc/RDDProcessManager.cpp
@@ -99,44 +99,49 @@ void RDDProcessManager::OnPreferenceChange(const char16_t* aData) {
   }
 }
 
-bool RDDProcessManager::EnsureRDDProcessAndCreateBridge(
-    base::ProcessId aOtherProcess,
-    mozilla::ipc::Endpoint<PRemoteDecoderManagerChild>*
-        aOutRemoteDecoderManager) {
-  bool success = false;
+auto RDDProcessManager::EnsureRDDProcessAndCreateBridge(
+    base::ProcessId aOtherProcess) -> RefPtr<EnsureRDDPromise> {
+  return InvokeAsync(GetMainThreadSerialEventTarget(), __func__,
+                     [aOtherProcess, this]() -> RefPtr<EnsureRDDPromise> {
+                       if (!Get()) {
+                         // Shutdown?
+                         return EnsureRDDPromise::CreateAndReject(
+                             NS_ERROR_NOT_AVAILABLE, __func__);
+                       }
+                       if (mProcess) {
+                         ipc::Endpoint<PRemoteDecoderManagerChild> endpoint;
+                         if (!CreateContentBridge(aOtherProcess, &endpoint)) {
+                           return EnsureRDDPromise::CreateAndReject(
+                               NS_ERROR_NOT_AVAILABLE, __func__);
+                         }
+                         return EnsureRDDPromise::CreateAndResolve(
+                             std::move(endpoint), __func__);
+                       }
 
-  RefPtr<Runnable> task =
-      NS_NewRunnableFunction("RDDProcessManager::RDDProcessManager", [&]() {
-        if (mProcess) {
-          success =
-              CreateContentBridge(aOtherProcess, aOutRemoteDecoderManager);
-          return;
-        }
+                       mNumProcessAttempts++;
 
-        mNumProcessAttempts++;
+                       std::vector<std::string> extraArgs;
+                       nsCString parentBuildID(mozilla::PlatformBuildID());
+                       extraArgs.push_back("-parentBuildID");
+                       extraArgs.push_back(parentBuildID.get());
 
-        std::vector<std::string> extraArgs;
-        nsCString parentBuildID(mozilla::PlatformBuildID());
-        extraArgs.push_back("-parentBuildID");
-        extraArgs.push_back(parentBuildID.get());
-
-        // The subprocess is launched asynchronously, so we wait for a callback
-        // to acquire the IPDL actor.
-        mProcess = new RDDProcessHost(this);
-        if (!mProcess->Launch(extraArgs)) {
-          DestroyProcess();
-          return;
-        }
-        if (!EnsureRDDReady()) {
-          return;
-        }
-
-        success = CreateVideoBridge() &&
-                  CreateContentBridge(aOtherProcess, aOutRemoteDecoderManager);
-      });
-  SyncRunnable::DispatchToThread(GetMainThreadSerialEventTarget(), task);
-
-  return success;
+                       // The subprocess is launched asynchronously, so we wait
+                       // for a callback to acquire the IPDL actor.
+                       mProcess = new RDDProcessHost(this);
+                       if (!mProcess->Launch(extraArgs)) {
+                         DestroyProcess();
+                         return EnsureRDDPromise::CreateAndReject(
+                             NS_ERROR_NOT_AVAILABLE, __func__);
+                       }
+                       ipc::Endpoint<PRemoteDecoderManagerChild> endpoint;
+                       if (!EnsureRDDReady() || !CreateVideoBridge() ||
+                           !CreateContentBridge(aOtherProcess, &endpoint)) {
+                         return EnsureRDDPromise::CreateAndReject(
+                             NS_ERROR_NOT_AVAILABLE, __func__);
+                       }
+                       return EnsureRDDPromise::CreateAndResolve(
+                           std::move(endpoint), __func__);
+                     });
 }
 
 bool RDDProcessManager::IsRDDProcessLaunching() {
@@ -237,27 +242,23 @@ void RDDProcessManager::DestroyProcess() {
 bool RDDProcessManager::CreateContentBridge(
     base::ProcessId aOtherProcess,
     ipc::Endpoint<PRemoteDecoderManagerChild>* aOutRemoteDecoderManager) {
-  bool success = false;
-  RefPtr<Runnable> task =
-      NS_NewRunnableFunction("RDDProcessManager::RDDProcessManager", [&]() {
-        ipc::Endpoint<PRemoteDecoderManagerParent> parentPipe;
-        ipc::Endpoint<PRemoteDecoderManagerChild> childPipe;
+  MOZ_ASSERT(NS_IsMainThread());
 
-        nsresult rv = PRemoteDecoderManager::CreateEndpoints(
-            mRDDChild->OtherPid(), aOtherProcess, &parentPipe, &childPipe);
-        if (NS_FAILED(rv)) {
-          MOZ_LOG(sPDMLog, LogLevel::Debug,
-                  ("Could not create content remote decoder: %d", int(rv)));
-          return;
-        }
+  ipc::Endpoint<PRemoteDecoderManagerParent> parentPipe;
+  ipc::Endpoint<PRemoteDecoderManagerChild> childPipe;
 
-        mRDDChild->SendNewContentRemoteDecoderManager(std::move(parentPipe));
+  nsresult rv = PRemoteDecoderManager::CreateEndpoints(
+      mRDDChild->OtherPid(), aOtherProcess, &parentPipe, &childPipe);
+  if (NS_FAILED(rv)) {
+    MOZ_LOG(sPDMLog, LogLevel::Debug,
+            ("Could not create content remote decoder: %d", int(rv)));
+    return false;
+  }
 
-        *aOutRemoteDecoderManager = std::move(childPipe);
-        success = true;
-      });
-  SyncRunnable::DispatchToThread(GetMainThreadSerialEventTarget(), task);
-  return success;
+  mRDDChild->SendNewContentRemoteDecoderManager(std::move(parentPipe));
+
+  *aOutRemoteDecoderManager = std::move(childPipe);
+  return true;
 }
 
 bool RDDProcessManager::CreateVideoBridge() {
diff --git a/dom/media/ipc/RDDProcessManager.h b/dom/media/ipc/RDDProcessManager.h
index e00ed5e53296..ab0db1a9d5ee 100644
--- a/dom/media/ipc/RDDProcessManager.h
+++ b/dom/media/ipc/RDDProcessManager.h
@@ -5,13 +5,14 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #ifndef _include_dom_media_ipc_RDDProcessManager_h_
 #define _include_dom_media_ipc_RDDProcessManager_h_
+#include "mozilla/MozPromise.h"
+#include "mozilla/PRemoteDecoderManagerChild.h"
 #include "mozilla/RDDProcessHost.h"
 #include "mozilla/ipc/TaskFactory.h"
 
 namespace mozilla {
 
 class MemoryReportingProcess;
-class PRemoteDecoderManagerChild;
 class RDDChild;
 
 // The RDDProcessManager is a singleton responsible for creating RDD-bound
@@ -27,18 +28,12 @@ class RDDProcessManager final : public RDDProcessHost::Listener {
 
   ~RDDProcessManager();
 
+  using EnsureRDDPromise =
+      MozPromise<ipc::Endpoint<PRemoteDecoderManagerChild>, nsresult, true>;
   // If not using a RDD process, launch a new RDD process asynchronously and
   // create a RemoteDecoderManager bridge
-  bool EnsureRDDProcessAndCreateBridge(
-      base::ProcessId aOtherProcess,
-      mozilla::ipc::Endpoint<PRemoteDecoderManagerChild>*
-          aOutRemoteDecoderManager);
-  bool IsRDDProcessLaunching();
-
-  // Ensure that RDD-bound methods can be used. If no RDD process is being
-  // used, or one is launched and ready, this function returns immediately.
-  // Otherwise it blocks until the RDD process has finished launching.
-  bool EnsureRDDReady();
+  RefPtr<EnsureRDDPromise> EnsureRDDProcessAndCreateBridge(
+      base::ProcessId aOtherProcess);
 
   void OnProcessLaunchComplete(RDDProcessHost* aHost) override;
   void OnProcessUnexpectedShutdown(RDDProcessHost* aHost) override;
@@ -67,6 +62,11 @@ class RDDProcessManager final : public RDDProcessHost::Listener {
   RDDProcessHost* Process() { return mProcess; }
 
  private:
+  bool IsRDDProcessLaunching();
+  // Ensure that RDD-bound methods can be used. If no RDD process is being
+  // used, or one is launched and ready, this function returns immediately.
+  // Otherwise it blocks until the RDD process has finished launching.
+  bool EnsureRDDReady();
   bool CreateVideoBridge();
 
   // Called from our xpcom-shutdown observer.
@@ -94,13 +94,12 @@ class RDDProcessManager final : public RDDProcessHost::Listener {
   };
   friend class Observer;
 
- private:
-  bool CreateContentBridge(base::ProcessId aOtherProcess,
-                           mozilla::ipc::Endpoint<PRemoteDecoderManagerChild>*
-                               aOutRemoteDecoderManager);
+  bool CreateContentBridge(
+      base::ProcessId aOtherProcess,
+      ipc::Endpoint<PRemoteDecoderManagerChild>* aOutRemoteDecoderManager);
 
   const RefPtr<Observer> mObserver;
-  mozilla::ipc::TaskFactory<RDDProcessManager> mTaskFactory;
+  ipc::TaskFactory<RDDProcessManager> mTaskFactory;
   uint32_t mNumProcessAttempts = 0;
 
   // Fields that are associated with the current RDD process.
@@ -110,7 +109,7 @@ class RDDProcessManager final : public RDDProcessHost::Listener {
   // Collects any pref changes that occur during process launch (after
   // the initial map is passed in command-line arguments) to be sent
   // when the process can receive IPC messages.
-  nsTArray<mozilla::dom::Pref> mQueuedPrefs;
+  nsTArray<dom::Pref> mQueuedPrefs;
 };
 
 }  // namespace mozilla
diff --git a/ipc/glue/BackgroundParentImpl.cpp b/ipc/glue/BackgroundParentImpl.cpp
index 3e86d9dc4663..05462759a462 100644
--- a/ipc/glue/BackgroundParentImpl.cpp
+++ b/ipc/glue/BackgroundParentImpl.cpp
@@ -761,7 +761,7 @@ bool BackgroundParentImpl::DeallocPCamerasParent(
 }
 
 auto BackgroundParentImpl::AllocPUDPSocketParent(
-    const Maybe<PrincipalInfo>& /* unused */, const nsCString & /* unused */)
+    const Maybe<PrincipalInfo>& /* unused */, const nsCString& /* unused */)
     -> PUDPSocketParent* {
   RefPtr<UDPSocketParent> p = new UDPSocketParent(this);
 
@@ -1316,15 +1316,25 @@ mozilla::ipc::IPCResult
 BackgroundParentImpl::RecvEnsureRDDProcessAndCreateBridge(
     EnsureRDDProcessAndCreateBridgeResolver&& aResolver) {
   RDDProcessManager* rdd = RDDProcessManager::Get();
-  Endpoint<PRemoteDecoderManagerChild> endpoint;
-  nsresult rv =
-      rdd && rdd->EnsureRDDProcessAndCreateBridge(OtherPid(), &endpoint)
-          ? NS_OK
-          : NS_ERROR_NOT_AVAILABLE;
-  aResolver(
-      Tuple<const nsresult&, Endpoint<mozilla::PRemoteDecoderManagerChild>&&>(
-          rv, std::move(endpoint)));
-
+  using Type =
+      Tuple<const nsresult&, Endpoint<mozilla::PRemoteDecoderManagerChild>&&>;
+  if (!rdd) {
+    aResolver(
+        Type(NS_ERROR_NOT_AVAILABLE, Endpoint<PRemoteDecoderManagerChild>()));
+  } else {
+    rdd->EnsureRDDProcessAndCreateBridge(OtherPid())
+        ->Then(GetCurrentSerialEventTarget(), __func__,
+               [resolver = std::move(aResolver)](
+                   mozilla::RDDProcessManager::EnsureRDDPromise::
+                       ResolveOrRejectValue&& aValue) mutable {
+                 if (aValue.IsReject()) {
+                   resolver(Type(aValue.RejectValue(),
+                                 Endpoint<PRemoteDecoderManagerChild>()));
+                   return;
+                 }
+                 resolver(Type(NS_OK, std::move(aValue.ResolveValue())));
+               });
+  }
   return IPC_OK();
 }