Litmus is a 3rd Party service for testing web pages on an array of different web browsers.
http://litmusapp.com/alkaline/
To use the Litmus service with Flux, first download the Alkaline application from the above link and install it into your applications folder.
Also download the Coda plugin for Alkaline, and copy it into your Flux plugins folder. (You can easily open this folder by choosing the Open Plug-ins folder from Flux's Plug-ins menu.)
Flux supports many, but not all Coda plugins
For the plug-in to be recognized, you need to restart Flux.
You can now use the menu entries shown above, please note however, Litmus can only test 'online' pages, so you need to setup a custom URL in Flux, so Flux can tell Litmus where your page is on the web.
If you haven't setup a custom URL, Flux will prompt you to do so.
Once this has been setup, the menu entries will launch the Alkaline application and direct it to the URL you have specified for the page.