Class: SyncChromeSender
proxy.SyncChromeSender()
The SyncChromeSender sends synchronous RPC messages to the chrome context, using a frame's sendSyncMessage (nsISyncMessageSender) function.
Example on how to use from a frame content script:
let sender = new SyncChromeSender(sendSyncMessage.bind(this));
let res = sender.send("addCookie", cookie);