First of all congrats for this great extension!

Trying to send some details about the error to the client, I found out that the "error" field in response is automatically casted to string ( see. connection.js:104 ), although the "error" field in JSON RPC 2.0 should be an object (see http://www.jsonrpc.org/specification#error_object ) with "message", "code" and "data" subfields.