diff --git a/dom/clients/manager/ClientManagerService.cpp b/dom/clients/manager/ClientManagerService.cpp
index 5c36340c9e9f..709ecf0ee367 100644
--- a/dom/clients/manager/ClientManagerService.cpp
+++ b/dom/clients/manager/ClientManagerService.cpp
@@ -107,6 +107,10 @@ RefPtr<GenericPromise> OnShutdown() {
 
 }  // anonymous namespace
 
+ClientManagerService::FutureClientSourceParent::FutureClientSourceParent(
+    const IPCClientInfo& aClientInfo)
+    : mPrincipalInfo(aClientInfo.principalInfo()) {}
+
 ClientManagerService::ClientManagerService() : mShutdown(false) {
   AssertIsOnBackgroundThread();
 
diff --git a/dom/clients/manager/ClientManagerService.h b/dom/clients/manager/ClientManagerService.h
index 9f247b667427..eed2cb26c207 100644
--- a/dom/clients/manager/ClientManagerService.h
+++ b/dom/clients/manager/ClientManagerService.h
@@ -6,7 +6,12 @@
 #ifndef _mozilla_dom_ClientManagerService_h
 #define _mozilla_dom_ClientManagerService_h
 
+#include "ClientHandleParent.h"
 #include "ClientOpPromise.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/HashTable.h"
+#include "mozilla/MozPromise.h"
+#include "mozilla/Variant.h"
 #include "nsDataHashtable.h"
 
 namespace mozilla {
@@ -28,6 +33,55 @@ class ContentParent;
 // browser.  This service runs on the PBackground thread.  To interact
 // it with it please use the ClientManager and ClientHandle classes.
 class ClientManagerService final {
+  // Placeholder type that represents a ClientSourceParent that may be created
+  // in the future (e.g. while a redirect chain is being resolved).
+  //
+  // Each FutureClientSourceParent has a promise that callbacks may be chained
+  // to; the promise will be resolved when the associated ClientSourceParent is
+  // created or rejected when it's known that it'll never be created.
+  class FutureClientSourceParent {
+   public:
+    explicit FutureClientSourceParent(const IPCClientInfo& aClientInfo);
+
+    const mozilla::ipc::PrincipalInfo& PrincipalInfo() const {
+      return mPrincipalInfo;
+    }
+
+    already_AddRefed<SourcePromise> Promise() {
+      return mPromiseHolder.Ensure(__func__);
+    }
+
+    void ResolvePromiseIfExists(ClientSourceParent* aSource) {
+      MOZ_ASSERT(aSource);
+      mPromiseHolder.ResolveIfExists(aSource, __func__);
+    }
+
+    void RejectPromiseIfExists(const CopyableErrorResult& aRv) {
+      MOZ_ASSERT(aRv.Failed());
+      mPromiseHolder.RejectIfExists(aRv, __func__);
+    }
+
+   private:
+    const mozilla::ipc::PrincipalInfo mPrincipalInfo;
+    MozPromiseHolder<SourcePromise> mPromiseHolder;
+  };
+
+  using SourceTableEntry =
+      Variant<FutureClientSourceParent, ClientSourceParent*>;
+
+  struct nsIDHasher {
+    using Key = nsID;
+    using Lookup = Key;
+
+    static HashNumber hash(const Lookup& aLookup) {
+      return HashBytes(&aLookup, sizeof(Lookup));
+    }
+
+    static bool match(const Key& aKey, const Lookup& aLookup) {
+      return aKey.Equals(aLookup);
+    }
+  };
+
   // Store the ClientSourceParent objects in a hash table.  We want to
   // optimize for insertion, removal, and lookup by UUID.
   nsDataHashtable<nsIDHashKey, ClientSourceParent*> mSourceTable;
diff --git a/dom/clients/manager/moz.build b/dom/clients/manager/moz.build
index e2be201898f4..1dde94fc4b39 100644
--- a/dom/clients/manager/moz.build
+++ b/dom/clients/manager/moz.build
@@ -7,6 +7,7 @@
 EXPORTS.mozilla.dom += [
   'ClientChannelHelper.h',
   'ClientHandle.h',
+  'ClientHandleParent.h',
   'ClientInfo.h',
   'ClientIPCUtils.h',
   'ClientManager.h',