gistfile1.txt

// Run this
//     in Scratchpad
//     in the *target* Firefox
//     using Environment -> Browser
//     before opening the script debugger in the other Firefox.

Components.utils.import("resource://gre/modules/devtools/dbg-server.jsm");

function allowDebuggersToConnect() {
  const DEBUGGER_PORT = 60000;
  if (!DebuggerServer.initialized) {
    DebuggerServer.init();
    DebuggerServer.addBrowserActors();
  }
  DebuggerServer.openListener(DEBUGGER_PORT, false);
}

allowDebuggersToConnect();