I use the add on but in Google Chrome in combination with Abine and Do Not Track Plus, Disconnect and Collusion for Chrome.
Tracking is going on all the time, and a lot of the tracking goes on unnoticed, because the tracking extensions do not flag various trackers.
Web beacons, tiny 1 x 1 pixel so-called webbugs can be made visible but these extensions do not flag them. Obfuscated script tracking is also going under the radar, iframe detection is another aspect of tracking, so summa summarum I think these extensions only fundtioning "cosmetically".
Of course specific blocking (script blocking) and request policy extensions like Kiss Privacy will help, as does ABP with certain subscription lists & Better Pop up Blocker, but all these measures only bring partial protection against tracking, harvesting, clickfraud, etc. etc.
The only way that yolu are not being "profiled" is by not going to the Internet at all, because all the traces you leave behind browsing leave a very good impression to trackers of your online activities and interests,
polonus