WS Listener

A minimal Firefox extension that intercepts every WebSocket frame on the current page and lets you inspect and export them.

Features

Captures sent and received frames in real time, including binary (Blob / ArrayBuffer) messages
Tracks connection lifecycle events (open, close, error)
Filters by direction (sent / received / open-close) and free-text search
Detail panel with automatic JSON pretty-print
One-click export as JSON or CSV

How it works

injected.js          patches window.WebSocket inside the page context
     ↓  CustomEvent
content_script.js    bridges the page ↔ extension boundary
     ↓  runtime.sendMessage
background.js        stores frames per tab, notifies the popup
     ↓  runtime.sendMessage
popup.js             renders the UI and handles exports

The key constraint is that a content script runs in an isolated sandbox and cannot patch window.WebSocket directly. injected.js is loaded as a regular <script> tag so it executes in the page's own JavaScript context.

Installation (temporary, for development)

Open Firefox and navigate to about:debugging
Click This Firefox → Load Temporary Add-on…
Select the manifest.json file from this folder

The extension stays active until Firefox is restarted. For a permanent install, sign the extension via addons.mozilla.org.

Files

File	Role
`manifest.json`	Extension manifest (Manifest V2)
`injected.js`	WebSocket proxy injected into the page context
`content_script.js`	Injects the script and relays events to the background
`background.js`	Stores frames per tab and pushes updates to the popup
`popup.html`	Popup markup and styles
`popup.js`	Popup logic (rendering, filtering, export)

License

Limitations

Firefox only (uses browser.* APIs and Manifest V2 browser_action)
Frames sent before the content script runs (very early document_start code) may be missed on extremely fast connections
Binary frames are decoded as UTF-8 text via Blob.text()

Teyk0o/WSListener

README