Recent news has indicated that Google AdSense accounts are now being disabled for using a plug-in for Firefox that is called "Tamper Data Fix". If you want to stay involved with the AdSense program from Google, I would highly suggest staying away from this particular plug-in. You may see exactly what Tamper Data is by clicking on the following link: https://addons.mozilla.org/en-US/firefox/addon/966 . When an individual uses this particular add-on in Firefox, it permits them to make changes to the headers that are http or https based and even permits modifications to the parameters of a website post.
The reason Google AdSense is disabling accounts using this particular plug-in is because individuals are taking the program and changing their location. As a result, it displays more earnings in their account. Then, there are many that are using it in order to cover up their exact location when signing up for a Google AdSense account. Every single day, website owners that use AdSense are struggling in order to get high page rankings, backlinks, and visitors in order to increase their earnings with AdSense, so I personally believe that this is a positive move for Google. You can read more about this issue here: http://www.seroundtable.com/archives/021193.html