diff --git a/browser/base/content/test/trackingUI/browser.ini b/browser/base/content/test/trackingUI/browser.ini
index 252896d3e3bd..5adc7159a79f 100644
--- a/browser/base/content/test/trackingUI/browser.ini
+++ b/browser/base/content/test/trackingUI/browser.ini
@@ -29,7 +29,7 @@ support-files =
 [browser_trackingUI_open_preferences.js]
 [browser_trackingUI_pbmode_exceptions.js]
 [browser_trackingUI_report_breakage.js]
-skip-if = fission || os == 'linux' && (debug || asan) # Bug 1546797
+skip-if = skip-if = fission || debug || asan # Bug 1546797
 [browser_trackingUI_state.js]
 skip-if = serviceworker_e10s # see https://bugzilla.mozilla.org/show_bug.cgi?id=1511303#c1
 [browser_trackingUI_state_reset.js]
diff --git a/ipc/glue/MessageChannel.cpp b/ipc/glue/MessageChannel.cpp
index 0cb6e422920b..e596172b60a8 100644
--- a/ipc/glue/MessageChannel.cpp
+++ b/ipc/glue/MessageChannel.cpp
@@ -556,6 +556,18 @@ static void TryRegisterStrongMemoryReporter() {
 
 Atomic<size_t> MessageChannel::gUnresolvedResponses;
 
+// Channels in record/replay middleman processes can forward messages that
+// originated in a child recording process. Middleman processes are given
+// a large negative sequence number so that sequence numbers on their messages
+// can be distinguished from those on recording process messages.
+static const int32_t MiddlemanStartSeqno = -(1 << 30);
+
+/* static */
+bool MessageChannel::MessageOriginatesFromMiddleman(const Message& aMessage) {
+  MOZ_ASSERT(recordreplay::IsMiddleman());
+  return aMessage.seqno() < MiddlemanStartSeqno;
+}
+
 MessageChannel::MessageChannel(const char* aName, IToplevelProtocol* aListener)
     : mName(aName),
       mListener(aListener),
@@ -605,6 +617,10 @@ MessageChannel::MessageChannel(const char* aName, IToplevelProtocol* aListener)
 
   TryRegisterStrongMemoryReporter<PendingResponseReporter>();
   TryRegisterStrongMemoryReporter<ChannelCountReporter>();
+
+  if (recordreplay::IsMiddleman()) {
+    mNextSeqno = MiddlemanStartSeqno;
+  }
 }
 
 MessageChannel::~MessageChannel() {
diff --git a/ipc/glue/MessageChannel.h b/ipc/glue/MessageChannel.h
index 87e3810b7ce7..e3e7a5c4f48b 100644
--- a/ipc/glue/MessageChannel.h
+++ b/ipc/glue/MessageChannel.h
@@ -318,6 +318,10 @@ class MessageChannel : HasResultCodes, MessageLoop::DestructionObserver {
    */
   bool IsCrossProcess() const { return mIsCrossProcess; }
 
+  // Return whether a message definitely originated from a middleman process,
+  // due to its sequence number.
+  static bool MessageOriginatesFromMiddleman(const Message& aMessage);
+
 #ifdef OS_WIN
   struct MOZ_STACK_CLASS SyncStackFrame {
     SyncStackFrame(MessageChannel* channel, bool interrupt);
diff --git a/toolkit/recordreplay/ipc/ParentForwarding.cpp b/toolkit/recordreplay/ipc/ParentForwarding.cpp
index d3bf3bfae09a..5c78f3b9623c 100644
--- a/toolkit/recordreplay/ipc/ParentForwarding.cpp
+++ b/toolkit/recordreplay/ipc/ParentForwarding.cpp
@@ -140,6 +140,12 @@ static bool HandleMessageInMiddleman(ipc::Side aSide,
     return false;
   }
 
+  // Asynchronous replies to messages originally sent by the middleman need to
+  // be handled in the middleman.
+  if (ipc::MessageChannel::MessageOriginatesFromMiddleman(aMessage)) {
+    return true;
+  }
+
   return false;
 }