Bugzilla

Here is my finding.
1. I saw the first time GetOrCreateSocketActorForCurrentThread was called on non main thread.
2. [SendInitBackgroundRunnable](https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/ipc/glue/BackgroundImpl.cpp#1594) was created.
3. SendInitBackgroundRunnable was dispatched to [aMainEventTarget](https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/ipc/glue/BackgroundImpl.cpp#1626), which is mCallbackThread.
4. [bridgeChild->SendInitBackground](https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/ipc/glue/BackgroundImpl.cpp#1599) was never called. So, BackgroundParent was not created on socket process.
5. The third time that GetOrCreateSocketActorForCurrentThread was called on main thread, so SendInitBackground is directly called. I think that's the reason why I only see one MediaTransportParent was created on socket process.

Here is my finding.
1. I saw the first time GetOrCreateSocketActorForCurrentThread was called on non main thread.
2. [SendInitBackgroundRunnable](https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/ipc/glue/BackgroundImpl.cpp#1594) was created.
3. SendInitBackgroundRunnable was dispatched to [aMainEventTarget](https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/ipc/glue/BackgroundImpl.cpp#1626), which is mCallbackThread.
4. [bridgeChild->SendInitBackground](https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/ipc/glue/BackgroundImpl.cpp#1599) was never called. So, BackgroundParent was not created on socket process.
5. The third time that GetOrCreateSocketActorForCurrentThread was called on main thread, so SendInitBackground is directly called. I think that's the reason why I only see one MediaTransportParent was created on socket process.

Could you check why the runnable is never executed?