Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.

Link: http://getfirebug.com

With the help of this tool, you can edit the CSS of our StoreFront site, to customize the appearance of the site.

You can search the Backgroung Image for change it:

Or the panel properties for customice the elements:

You can change the Storefront properties using the custom file.

This configuration file is located on:

Any change in this file, replace the original config on default.htm.style.min.css

Resource:

For customize the Site, you can check the next post:

1. http://www.jeroentielen.nl/easy-customizingbranding-the-citrix-receiver-for-web/
2. http://blogs.citrix.com/2012/05/24/how-to-brand-citrix-receiver-for-web/