AdSense Preview Tool for Firefox. It basically just creates a pop up window showing what ads would appear on the web page you are looking at, if Google AdSense is used. Very useful for deciding whether you should put AdSense on your website. However it does not have localisation preview like the "official" preview tool, so I cannot see what the US readers have seen.
Another interesting use is, using this preview tool to see how Google categorises your website. On my index page, I got:
- Free Bible Study Course (who are United Church of God?)
- Apostolic Sermon Outlines (pentecostal sermons, yik!)
- Martin Luther King Jr. (biography software)
- Voice of the Martyrs (VoM Australia -- do they advertise as well?)
- Flying Colors (get rich quick via property scheme)
- Free Bible Software (enter Jesus survey and win $300, what?!)
Seems to be Christianity-biased, although less than a quarter of my posts are about church and Christianity. Still, more than half of those ads are dodgy, and now I feel sorry for those who have actually clicked on them.
Update: I actually wondered the same thing two and half years ago!