--- a/gfx/vr/VRManager.cpp
+++ b/gfx/vr/VRManager.cpp
@@ -90,17 +90,18 @@ VRManager::VRManager()
 
   // OSVR is cross platform compatible
   mgr = VRDisplayManagerOSVR::Create();
   if (mgr) {
       mManagers.AppendElement(mgr);
   }
 #endif
   // Enable gamepad extensions while VR is enabled.
-  if (gfxPrefs::VREnabled()) {
+  // Preference only can be set at the Parent process.
+  if (XRE_IsParentProcess() && gfxPrefs::VREnabled()) {
     Preferences::SetBool("dom.gamepad.extensions.enabled", true);
   }
 }
 
 VRManager::~VRManager()
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(!mInitialized);