Several web apps, such as Virgin Broadband activation, require you to have a “Windows or Mac” computer. Most of them only check the useragent string that your browser sends them so you can do the following to fool them:
1. Open firefox and type about:config in the address bar.
2. Type in general.useragent.extra.firefox in the filter bar.
3. Change the value of string above to Mozilla/4.0 (compatible: MSIE 7.0; Windows NT 6.0).
4. Restart Firefox.
It worked to get Virgin Broadband activation web app going on my Ubuntu netbook and it’s a good trick to try whenever a web app tells you you need a different OS.