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WebSocket Monitor

This extension is not supported in Firefox 57+ and we are planning to rewrite it on top of new WebExtension API. There is already an experimental prototype, but more work needed to make it useful. See issue 75 for more details

WebSocket monitor is an extension to Firefox developer tools that can be used to monitor WebSocket connections in Firefox. It allows inspecting all data sent and received.

See Home Page for more details

This is the source code, the extension can be downloaded here.


  1. Install the extension
  2. Open a browser tab and developer tools toolbox on it (F12)
  3. Select the Web Sockets toolbox panel
  4. Initiate WebSocket connection on the page and exchanges some messages.
  5. Check out content of the Web Sockets panel.

You might want to check out online demo page

Hacking on WebSocket Monitor

  1. Get npm

  2. Get JPM: sudo npm install -g jpm

  3. Get the WebSocketMonitor repo: git clone and install its dependencies via npm install

  4. Run jpm run -b <file path to your Firefox binary> --binary-args '' in the source directory to launch Firefox, which automatically creates a clean profile and launches the demo page.

If you wish to run it with an existing profile, first create a new profile via the Profile Manager, and then run jpm run -b <file path to your Firefox binary> -p <path to your Firefox profile (needs to start with /)>.

Further Resources