diff --git a/netwerk/ipc/NeckoChannelParams.ipdlh b/netwerk/ipc/NeckoChannelParams.ipdlh
index 85785ef3c45..315df68859a 100644
--- a/netwerk/ipc/NeckoChannelParams.ipdlh
+++ b/netwerk/ipc/NeckoChannelParams.ipdlh
@@ -116,6 +116,7 @@ struct HttpChannelOpenArgs
   nsCString                   schedulingContextID;
   OptionalCorsPreflightArgs   preflightArgs;
   uint32_t                    initialRwin;
+  bool                        suspendAfterSynthesizeResponse;
 };
 
 struct HttpChannelConnectArgs
diff --git a/netwerk/protocol/http/HttpChannelChild.cpp b/netwerk/protocol/http/HttpChannelChild.cpp
index 2e74772c476..e5fdfd5f52f 100644
--- a/netwerk/protocol/http/HttpChannelChild.cpp
+++ b/netwerk/protocol/http/HttpChannelChild.cpp
@@ -188,6 +188,7 @@ HttpChannelChild::HttpChannelChild()
   , mShouldInterceptSubsequentRedirect(false)
   , mRedirectingForSubsequentSynthesizedResponse(false)
   , mShouldParentIntercept(false)
+  , mSuspendParentAfterSynthesizeResponse(false)
 {
   LOG(("Creating HttpChannelChild @%x\n", this));
 
@@ -1889,8 +1890,11 @@ HttpChannelChild::ContinueAsyncOpen()
 
   if (mResponseHead) {
     openArgs.synthesizedResponseHead() = *mResponseHead;
+    openArgs.suspendAfterSynthesizeResponse() =
+      mSuspendParentAfterSynthesizeResponse;
   } else {
     openArgs.synthesizedResponseHead() = mozilla::void_t();
+    openArgs.suspendAfterSynthesizeResponse() = false;
   }
 
   nsCOMPtr<nsISerializable> secInfoSer = do_QueryInterface(mSecurityInfo);
@@ -2425,6 +2429,7 @@ HttpChannelChild::DivertToParent(ChannelDiverterChild **aChild)
   // yet.  We need one, though, in order to have a parent side to divert to.
   // Therefore, create the actor just in time for us to suspend and divert it.
   if (mSynthesizedResponse && !RemoteChannelExists()) {
+    mSuspendParentAfterSynthesizeResponse = true;
     rv = ContinueAsyncOpen();
     NS_ENSURE_SUCCESS(rv, rv);
   }
diff --git a/netwerk/protocol/http/HttpChannelChild.h b/netwerk/protocol/http/HttpChannelChild.h
index 228a0875e9a..8d3f32cfe0a 100644
--- a/netwerk/protocol/http/HttpChannelChild.h
+++ b/netwerk/protocol/http/HttpChannelChild.h
@@ -231,6 +231,10 @@ private:
   // before the network transaction is initiated.
   bool mShouldParentIntercept;
 
+  // Set if the corresponding parent channel should suspend after a response
+  // is synthesized.
+  bool mSuspendParentAfterSynthesizeResponse;
+
   // true after successful AsyncOpen until OnStopRequest completes.
   bool RemoteChannelExists() { return mIPCOpen && !mKeptAlive; }
 
diff --git a/netwerk/protocol/http/HttpChannelParent.cpp b/netwerk/protocol/http/HttpChannelParent.cpp
index 26e12f094bc..85600f693bc 100644
--- a/netwerk/protocol/http/HttpChannelParent.cpp
+++ b/netwerk/protocol/http/HttpChannelParent.cpp
@@ -66,6 +66,7 @@ HttpChannelParent::HttpChannelParent(const PBrowserOrId& iframeEmbedding,
   , mSuspendedForDiversion(false)
   , mShouldIntercept(false)
   , mShouldSuspendIntercept(false)
+  , mSuspendAfterSynthesizeResponse(false)
   , mNestedFrameId(0)
 {
   LOG(("Creating HttpChannelParent [this=%p]\n", this));
@@ -132,7 +133,7 @@ HttpChannelParent::Init(const HttpChannelCreationArgs& aArgs)
                        a.loadInfo(), a.synthesizedResponseHead(),
                        a.synthesizedSecurityInfoSerialization(),
                        a.cacheKey(), a.schedulingContextID(), a.preflightArgs(),
-                       a.initialRwin());
+                       a.initialRwin(), a.suspendAfterSynthesizeResponse());
   }
   case HttpChannelCreationArgs::THttpChannelConnectArgs:
   {
@@ -276,6 +277,14 @@ HttpChannelParent::SynthesizeResponse(nsIInterceptedChannel* aChannel)
 
   mSynthesizedResponseHead = nullptr;
 
+  // Suspend now even though the FinishSynthesizeResponse runnable has
+  // not executed.  We want to suspend after we get far enough to trigger
+  // the synthesis, but not actually allow the nsHttpChannel to trigger
+  // any OnStartRequests().
+  if (mSuspendAfterSynthesizeResponse) {
+    mChannel->Suspend();
+  }
+
   MaybeFlushPendingDiversion();
 }
 
@@ -376,7 +385,8 @@ HttpChannelParent::DoAsyncOpen(  const URIParams&           aURI,
                                  const uint32_t&            aCacheKey,
                                  const nsCString&           aSchedulingContextID,
                                  const OptionalCorsPreflightArgs& aCorsPreflightArgs,
-                                 const uint32_t&            aInitialRwin)
+                                 const uint32_t&            aInitialRwin,
+                                 const bool&                aSuspendAfterSynthesizeResponse)
 {
   nsCOMPtr<nsIURI> uri = DeserializeURI(aURI);
   if (!uri) {
@@ -589,6 +599,8 @@ HttpChannelParent::DoAsyncOpen(  const URIParams&           aURI,
   schedulingContextID.Parse(aSchedulingContextID.BeginReading());
   mChannel->SetSchedulingContextID(schedulingContextID);
 
+  mSuspendAfterSynthesizeResponse = aSuspendAfterSynthesizeResponse;
+
   if (loadInfo && loadInfo->GetEnforceSecurity()) {
     rv = mChannel->AsyncOpen2(mParentListener);
   }
diff --git a/netwerk/protocol/http/HttpChannelParent.h b/netwerk/protocol/http/HttpChannelParent.h
index 0fee2e70ed5..f75fc1b9268 100644
--- a/netwerk/protocol/http/HttpChannelParent.h
+++ b/netwerk/protocol/http/HttpChannelParent.h
@@ -128,7 +128,8 @@ protected:
                    const uint32_t&            aCacheKey,
                    const nsCString&           aSchedulingContextID,
                    const OptionalCorsPreflightArgs& aCorsPreflightArgs,
-                   const uint32_t&            aInitialRwin);
+                   const uint32_t&            aInitialRwin,
+                   const bool&                aSuspendAfterSynthesizeResponse);
 
   virtual bool RecvSetPriority(const uint16_t& priority) override;
   virtual bool RecvSetClassOfService(const uint32_t& cos) override;
@@ -238,6 +239,8 @@ private:
   bool mShouldIntercept : 1;
   // Set if this channel should suspend on interception.
   bool mShouldSuspendIntercept : 1;
+  // Set if this channel should be suspended after synthesizing a response.
+  bool mSuspendAfterSynthesizeResponse : 1;
 
   dom::TabId mNestedFrameId;