diff --git a/dom/ipc/ContentParent.cpp b/dom/ipc/ContentParent.cpp
index c753834957b4..6db159c11f73 100644
--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -142,6 +142,7 @@
 #include "nsIMutable.h"
 #include "nsINSSU2FToken.h"
 #include "nsIObserverService.h"
+#include "nsIParentChannel.h"
 #include "nsIPresShell.h"
 #include "nsIRemoteWindowContext.h"
 #include "nsIScriptError.h"
@@ -4419,6 +4420,32 @@ ContentParent::RecvLoadURIExternal(const URIParams& uri,
   return true;
 }
 
+bool
+ContentParent::RecvExtProtocolChannelConnectParent(const uint32_t& registrarId)
+{
+  nsresult rv;
+
+  // First get the real channel created before redirect on the parent.
+  nsCOMPtr<nsIChannel> channel;
+  rv = NS_LinkRedirectChannels(registrarId, nullptr, getter_AddRefs(channel));
+  NS_ENSURE_SUCCESS(rv, true);
+
+  nsCOMPtr<nsIParentChannel> parent = do_QueryInterface(channel, &rv);
+  NS_ENSURE_SUCCESS(rv, true);
+
+  // The channel itself is its own (faked) parent, link it.
+  rv = NS_LinkRedirectChannels(registrarId, parent, getter_AddRefs(channel));
+  NS_ENSURE_SUCCESS(rv, true);
+
+  // Signal the parent channel that it's a redirect-to parent.  This will
+  // make AsyncOpen on it do nothing (what we want).
+  // Yes, this is a bit of a hack, but I don't think it's necessary to invent
+  // a new interface just to set this flag on the channel.
+  parent->SetParentListener(nullptr);
+
+  return true;
+}
+
 bool
 ContentParent::HasNotificationPermission(const IPC::Principal& aPrincipal)
 {
diff --git a/dom/ipc/ContentParent.h b/dom/ipc/ContentParent.h
index f6d7d7bea333..ba7881f4f34c 100644
--- a/dom/ipc/ContentParent.h
+++ b/dom/ipc/ContentParent.h
@@ -1004,6 +1004,7 @@ private:
 
   virtual bool RecvLoadURIExternal(const URIParams& uri,
                                    PBrowserParent* windowContext) override;
+  virtual bool RecvExtProtocolChannelConnectParent(const uint32_t& registrarId) override;
 
   virtual bool RecvSyncMessage(const nsString& aMsg,
                                const ClonedMessageData& aData,
diff --git a/dom/ipc/PContent.ipdl b/dom/ipc/PContent.ipdl
index ebcbdad0e77a..64c33a1e17c3 100644
--- a/dom/ipc/PContent.ipdl
+++ b/dom/ipc/PContent.ipdl
@@ -833,6 +833,7 @@ parent:
     async SetURITitle(URIParams uri, nsString title);
 
     async LoadURIExternal(URIParams uri, PBrowser windowContext);
+    async ExtProtocolChannelConnectParent(uint32_t registrarId);
 
     // PrefService message
     sync ReadPrefsArray() returns (PrefSetting[] prefs) verify;
diff --git a/uriloader/exthandler/nsExternalProtocolHandler.cpp b/uriloader/exthandler/nsExternalProtocolHandler.cpp
index e9b397d14ff0..c570e2340f90 100644
--- a/uriloader/exthandler/nsExternalProtocolHandler.cpp
+++ b/uriloader/exthandler/nsExternalProtocolHandler.cpp
@@ -26,6 +26,8 @@
 // used to dispatch urls to default protocol handlers
 #include "nsCExternalHandlerService.h"
 #include "nsIExternalProtocolService.h"
+#include "nsIChildChannel.h"
+#include "nsIParentChannel.h"
 
 class nsILoadInfo;
 
@@ -34,12 +36,18 @@ class nsILoadInfo;
 // to calls in the OS for loading the url.
 ////////////////////////////////////////////////////////////////////////
 
-class nsExtProtocolChannel : public nsIChannel
+class nsExtProtocolChannel : public nsIChannel,
+                             public nsIChildChannel,
+                             public nsIParentChannel
 {
 public:
     NS_DECL_THREADSAFE_ISUPPORTS
     NS_DECL_NSICHANNEL
+    NS_DECL_NSIREQUESTOBSERVER
+    NS_DECL_NSISTREAMLISTENER
     NS_DECL_NSIREQUEST
+    NS_DECL_NSICHILDCHANNEL
+    NS_DECL_NSIPARENTCHANNEL
 
     nsExtProtocolChannel(nsIURI* aURI, nsILoadInfo* aLoadInfo);
 
@@ -54,6 +62,11 @@ private:
     nsresult mStatus;
     nsLoadFlags mLoadFlags;
     bool mWasOpened;
+    // Set true (as a result of ConnectParent invoked from child process)
+    // when this channel is on the parent process and is being used as
+    // a redirect target channel.  It turns AsyncOpen into a no-op since
+    // we do it on the child.
+    bool mConnectedParent;
     
     nsCOMPtr<nsIInterfaceRequestor> mCallbacks;
     nsCOMPtr<nsILoadGroup> mLoadGroup;
@@ -67,6 +80,10 @@ NS_INTERFACE_MAP_BEGIN(nsExtProtocolChannel)
    NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIChannel)
    NS_INTERFACE_MAP_ENTRY(nsIChannel)
    NS_INTERFACE_MAP_ENTRY(nsIRequest)
+   NS_INTERFACE_MAP_ENTRY(nsIChildChannel)
+   NS_INTERFACE_MAP_ENTRY(nsIParentChannel)
+   NS_INTERFACE_MAP_ENTRY(nsIStreamListener)
+   NS_INTERFACE_MAP_ENTRY(nsIRequestObserver)
 NS_INTERFACE_MAP_END_THREADSAFE
 
 nsExtProtocolChannel::nsExtProtocolChannel(nsIURI* aURI,
@@ -75,6 +92,7 @@ nsExtProtocolChannel::nsExtProtocolChannel(nsIURI* aURI,
   , mOriginalURI(aURI)
   , mStatus(NS_OK)
   , mWasOpened(false)
+  , mConnectedParent(false)
   , mLoadInfo(aLoadInfo)
 {
 }
@@ -184,6 +202,10 @@ NS_IMETHODIMP nsExtProtocolChannel::Open2(nsIInputStream** aStream)
 
 NS_IMETHODIMP nsExtProtocolChannel::AsyncOpen(nsIStreamListener *listener, nsISupports *ctxt)
 {
+  if (mConnectedParent) {
+    return NS_OK;
+  }
+
   MOZ_ASSERT(!mLoadInfo ||
              mLoadInfo->GetSecurityMode() == 0 ||
              mLoadInfo->GetInitialSecurityCheckDone() ||
@@ -338,6 +360,81 @@ NS_IMETHODIMP nsExtProtocolChannel::Resume()
   return NS_ERROR_NOT_IMPLEMENTED;
 }
 
+///////////////////////////////////////////////////////////////////////
+// From nsIChildChannel
+//////////////////////////////////////////////////////////////////////
+
+NS_IMETHODIMP nsExtProtocolChannel::ConnectParent(uint32_t registrarId)
+{
+  mozilla::dom::ContentChild::GetSingleton()->
+    SendExtProtocolChannelConnectParent(registrarId);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsExtProtocolChannel::CompleteRedirectSetup(nsIStreamListener *listener,
+                                                          nsISupports *context)
+{
+  // For redirects to external protocols we AsyncOpen on the child
+  // (not the parent) because child channel has the right docshell
+  // (which is needed for the select dialog).
+  return AsyncOpen(listener, context);
+}
+
+///////////////////////////////////////////////////////////////////////
+// From nsIParentChannel (derives from nsIStreamListener)
+//////////////////////////////////////////////////////////////////////
+
+NS_IMETHODIMP nsExtProtocolChannel::SetParentListener(HttpChannelParentListener* aListener)
+{
+  // This is called as part of the connect parent operation from
+  // ContentParent::RecvExtProtocolChannelConnectParent.  Setting
+  // this flag tells this channel to not proceed and makes AsyncOpen
+  // just no-op.  Actual operation will happen from the child process
+  // via CompleteRedirectSetup call on the child channel.
+  mConnectedParent = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsExtProtocolChannel::NotifyTrackingProtectionDisabled()
+{
+  // nothing to do
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsExtProtocolChannel::Delete()
+{
+  // nothing to do
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsExtProtocolChannel::OnStartRequest(nsIRequest *aRequest,
+                                                   nsISupports *aContext)
+{
+  // no data is expected
+  MOZ_CRASH("No data expected from external protocol channel");
+  return NS_ERROR_UNEXPECTED;
+}
+
+NS_IMETHODIMP nsExtProtocolChannel::OnStopRequest(nsIRequest *aRequest,
+                                                  nsISupports *aContext,
+                                                  nsresult aStatusCode)
+{
+  // no data is expected
+  MOZ_CRASH("No data expected from external protocol channel");
+  return NS_ERROR_UNEXPECTED;
+}
+
+NS_IMETHODIMP nsExtProtocolChannel::OnDataAvailable(nsIRequest *aRequest,
+                                                    nsISupports *aContext,
+                                                    nsIInputStream *aInputStream,
+                                                    uint64_t aOffset,
+                                                    uint32_t aCount)
+{
+  // no data is expected
+  MOZ_CRASH("No data expected from external protocol channel");
+  return NS_ERROR_UNEXPECTED;
+}
+
 ///////////////////////////////////////////////////////////////////////
 // the default protocol handler implementation
 //////////////////////////////////////////////////////////////////////