diff --git a/dom/media/webspeech/synth/pico/nsPicoService.cpp b/dom/media/webspeech/synth/pico/nsPicoService.cpp
index 2e2e2820e92..718cfd1edea 100644
--- a/dom/media/webspeech/synth/pico/nsPicoService.cpp
+++ b/dom/media/webspeech/synth/pico/nsPicoService.cpp
@@ -17,7 +17,7 @@
 #include "nsIFile.h"
 #include "nsThreadUtils.h"
 #include "prenv.h"
-
+#include "mozilla/Preferences.h"
 #include "mozilla/DebugOnly.h"
 #include <dlfcn.h>
 
@@ -453,6 +453,11 @@ nsPicoService::Observe(nsISupports* aSubject, const char* aTopic,
   MOZ_ASSERT(NS_IsMainThread());
   NS_ENSURE_TRUE(!strcmp(aTopic, "profile-after-change"), NS_ERROR_UNEXPECTED);
 
+  if (!Preferences::GetBool("media.webspeech.synth.enabled") ||
+      Preferences::GetBool("media.webspeech.synth.test")) {
+    return NS_OK;
+  }
+
   DebugOnly<nsresult> rv = NS_NewNamedThread("Pico Worker", getter_AddRefs(mThread));
   MOZ_ASSERT(NS_SUCCEEDED(rv));
   return mThread->Dispatch(
diff --git a/testing/profiles/prefs_general.js b/testing/profiles/prefs_general.js
index 033ccba9264..64aed3c2769 100644
--- a/testing/profiles/prefs_general.js
+++ b/testing/profiles/prefs_general.js
@@ -318,3 +318,6 @@ user_pref("browser.devedition.theme.enabled", false);
 
 // Disable periodic updates of service workers.
 user_pref("dom.serviceWorkers.periodic-updates.enabled", false);
+
+// Enable speech synth test service, and disable built in platform services.
+user_pref("media.webspeech.synth.test", true);