diff --git a/remote/RemoteAgent.jsm b/remote/RemoteAgent.jsm
index f99d6797b859..84553fd8e29a 100644
--- a/remote/RemoteAgent.jsm
+++ b/remote/RemoteAgent.jsm
@@ -221,7 +221,10 @@ class RemoteAgentClass {
   // XPCOM
 
   get QueryInterface() {
-    return ChromeUtils.generateQI([Ci.nsICommandLineHandler]);
+    return ChromeUtils.generateQI([
+      Ci.nsICommandLineHandler,
+      Ci.nsIRemoteAgent,
+    ]);
   }
 }
 
diff --git a/remote/moz.build b/remote/moz.build
index 35de24b09bef..b37adad2c6db 100644
--- a/remote/moz.build
+++ b/remote/moz.build
@@ -9,6 +9,9 @@ DIRS += [
 XPCOM_MANIFESTS += ["components.conf"]
 JAR_MANIFESTS += ["jar.mn"]
 
+XPIDL_MODULE = "remote"
+XPIDL_SOURCES += ["nsIRemoteAgent.idl"]
+
 with Files("**"):
     BUG_COMPONENT = ("Remote Protocol", "Agent")
 with Files("domains/**/Emulation.jsm"):
diff --git a/remote/nsIRemoteAgent.idl b/remote/nsIRemoteAgent.idl
new file mode 100644
index 000000000000..7e26ea959a54
--- /dev/null
+++ b/remote/nsIRemoteAgent.idl
@@ -0,0 +1,44 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+/**
+ * The Gecko remote agent is an RPC subsystem that exposes
+ * browser-internal interfaces and services to the surrounding
+ * system.
+ *
+ * Consumers, whether remote or browser-local, can interface with
+ * the browser through an assorted set of services ranging from
+ * document introspection and script evaluation, to instrumentation,
+ * user interaction simulation, and event subscription.
+ */
+[scriptable, uuid(8f685a9d-8181-46d6-a71d-869289099c6d)]
+interface nsIRemoteAgent : nsISupports
+{
+  /**
+   * Whether the remote agent is currently listening for new,
+   * incoming connections.
+   */
+  readonly attribute boolean listening;
+
+  /**
+   * Asynchronously starts the remote agent, and listens for new
+   * connections.
+   *
+   * The address must be a fully qualified URL that uses the "http://"
+   * scheme, and can optionally include a desired port.  If no port
+   * is chosen, the default port 9222 is used.
+   *
+   * If the requested port is 0, the system will atomically allocate
+   * a port.
+   *
+   * A "remote-listening" system observer notification with the URL
+   * of the main target's WebSocket will be emitted once listening.
+   */
+  void listen(in AString aURL);
+
+  /** Stops listening and drops existing connections. */
+  void close();
+};