How to view WS/WSS Websocket request content using Firebug or other?

Try Chrome's developer tools,

1. click 'Network' tab
2. use the filters at the bottom to show only WebSocket connections),
3. select the desired websocket connection,
4. note that there are 'Headers', 'Preview', 'Response', etc. sub-tabs to the right,
5. once data starts flowing a 'WebSocket Frames' subtab will appear. All data going in either direction is logged. Very informative.

As of 3, September 2014, it seems that WebSocket debugging in FireBug is in the hose : https://getfirebug.com/wiki/index.php/Firebug_2.0_Roadmap#Feature_Overview. But no release date is mentioned.

Update 2019-09-19

See this interesting Mozilla Hacks article.

Update 2017-11-24 The plugin system in Firefox changed. Websocket Monitor is at the moment of writing unavailable :(

Update 2016-04-06

WebSocket debugging in Firefox is finally possible using the Websocket Monitor addon for the Firefox Dev Tools! It is developed by the Firebug development team and its sources can be found here.

Update 2015-10-28

Jeff Griffiths, Product Manager for Firefox Developer Tools:

platform support is in nightly today & a prototype add-on is being worked on here: https://github.com/firebug/websocket-monitor

https://twitter.com/canuckistani/status/659399140590284800

Relevant feature request on the Firefox Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1203802

Update as of 2015-04-08

Fiddler 4.5 can now inspect WebSocket traffic natively.

Update 2014-09-11

Regarding this comment on the Firebug issue tracker :

It's currently off the radar as the Firebug team is working on integrating Firebug with the DevTools at the moment. This means it will be able to reuse the features provided by the built-in DevTools. You may therefore follow https://bugzil.la/885508.

The current version of Fiddler works just fine with WebSocket traffic. See http://blogs.msdn.com/b/fiddler/archive/2011/11/22/fiddler-and-websockets.aspx

See http://blogs.telerik.com/fiddler/posts/13-06-04/what-s-new-in-fiddler-2-4-4-5 for how to put the data on the Log tab.

To display data on a WebSockets tab,

you need an extension (this is slated to be built-in for version 2.5). For now, you can grab the current bits. Simply extract the ZIP and put the two files into the \Fiddler2\Scripts folder and restart Fiddler. If you double-click on a WebSocket session in Fiddler’s WebSessions list, the WebSockets tab will appear

There is WebSocket Monitor - an extension for Firefox developer tools that can be used to monitor WebSocket connections

After the extension is installed, open Firefox Developer Tools and switch to 'Web Sockets' panel. It's displaying WS frame traffic for the current page. There is an extra support for the following protocols:

• Socket IO
• SockJS
• WAMP
• Plain JSON

Not as comfortable as the other options mentioned here, but a universal tool that can help you in various situations: Use wireshark. With some knowledge about TCP you can debug problems that the other tools mentioned can not solve (unexpected disconnections, ...), because they work on a level that's too high. You can also (just as in Firebug, etc) read the actual websocket messages.

The disadvantage of wireshark is that it's rather cumbersome to work with encrypted connections.

Give it a try, I use it all the time to debug a Rails app which communicates with a Python websocket backend.