--- a/tools/profiler/gecko/PProfiler.ipdl
+++ b/tools/profiler/gecko/PProfiler.ipdl
@@ -13,16 +13,17 @@ namespace mozilla {
 // those processes.
 // It is a top-level protocol so that its child endpoint can be on a
 // background thread, so that profiles can be gathered even if the main thread
 // is unresponsive.
 async protocol PProfiler
 {
 child:
   async Start(ProfilerInitParams params);
+  async EnsureStarted(ProfilerInitParams params);
   async Stop();
   async Pause();
   async Resume();
 
   async GatherProfile() returns (nsCString profile);
 };
 
 } // namespace mozilla

--- a/tools/profiler/gecko/ProfilerChild.cpp
+++ b/tools/profiler/gecko/ProfilerChild.cpp
@@ -34,16 +34,31 @@ ProfilerChild::RecvStart(const ProfilerI
                  params.features(),
                  filterArray.Elements(),
                  filterArray.Length());
 
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
+ProfilerChild::RecvEnsureStarted(const ProfilerInitParams& params)
+{
+  nsTArray<const char*> filterArray;
+  for (size_t i = 0; i < params.filters().Length(); ++i) {
+    filterArray.AppendElement(params.filters()[i].get());
+  }
+
+  profiler_ensure_started(params.entries(), params.interval(),
+                          params.features(),
+                          filterArray.Elements(), filterArray.Length());
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult
 ProfilerChild::RecvStop()
 {
   profiler_stop();
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
 ProfilerChild::RecvPause()

--- a/tools/profiler/gecko/ProfilerParent.cpp
+++ b/tools/profiler/gecko/ProfilerParent.cpp
@@ -124,16 +124,44 @@ ProfilerParent::ProfilerParent()
 }
 
 void
 ProfilerParent::Init()
 {
   MOZ_RELEASE_ASSERT(NS_IsMainThread());
 
   ProfilerParentTracker::StartTracking(this);
+
+  // We propagated the profiler state from the parent process to the child
+  // process through MOZ_PROFILER_STARTUP* environment variables.
+  // However, the profiler state might have changed in this process since then,
+  // and now that an active communication channel has been established with the
+  // child process, it's a good time to sync up the two profilers again.
+
+  int entries = 0;
+  double interval = 0;
+  mozilla::Vector<const char*> filters;
+  uint32_t features;
+  profiler_get_start_params(&entries, &interval, &features, &filters);
+
+  if (entries != 0) {
+    ProfilerInitParams ipcParams;
+    ipcParams.enabled() = true;
+    ipcParams.entries() = entries;
+    ipcParams.interval() = interval;
+    ipcParams.features() = features;
+
+    for (uint32_t i = 0; i < filters.length(); ++i) {
+      ipcParams.filters().AppendElement(filters[i]);
+    }
+
+    Unused << SendEnsureStarted(ipcParams);
+  } else {
+    Unused << SendStop();
+  }
 }
 
 ProfilerParent::~ProfilerParent()
 {
   MOZ_COUNT_DTOR(ProfilerParent);
 
   MOZ_RELEASE_ASSERT(NS_IsMainThread());
   ProfilerParentTracker::StopTracking(this);

--- a/tools/profiler/public/ProfilerChild.h
+++ b/tools/profiler/public/ProfilerChild.h
@@ -31,16 +31,17 @@ class ProfilerChild final : public PProf
   nsCString GrabShutdownProfile();
 
   void Destroy();
 
 private:
   virtual ~ProfilerChild();
 
   mozilla::ipc::IPCResult RecvStart(const ProfilerInitParams& params) override;
+  mozilla::ipc::IPCResult RecvEnsureStarted(const ProfilerInitParams& params) override;
   mozilla::ipc::IPCResult RecvStop() override;
   mozilla::ipc::IPCResult RecvPause() override;
   mozilla::ipc::IPCResult RecvResume() override;
   mozilla::ipc::IPCResult RecvGatherProfile(GatherProfileResolver&& aResolve) override;
 
   void ActorDestroy(ActorDestroyReason aActorDestroyReason) override;
 
   nsCOMPtr<nsIThread> mThread;