The opt-out cookie model is a joke. There are 90+ behavioral advertising companies, and consumers must opt-out of each one in order to just say no.
Tools like TACO help, but they simply do not scale. Each time a new advertiser hits the market, TACO must be updated to support its opt-out. As a result, the privacy community is always playing catch-up. It's time to change that.
A much better approach is for a universal opt-out header, which the user could select with a single preference, and which would then be communicated to all web sites that they visit. If the site is an advertising company, they will hopefully honor the opt-out, and if they're not, they can ignore it. No harm done.
This tool acts as an implementation of exactly this, much in the same way Firefox 4 will. After the add-on has been installed, Firefox will send the following header along with every new request (HTTP or HTTPS) to a web server:
Pre-1.0 versions of this add-on:
Version 1.0 of this add-on:
NOTE: version 1.0 has changed to mimic the header supported by Firefox 4.0b11 and later, as well as the header sent by NoScript and recommended by donottrack.us. The meaning of the two opt-out headers sent before are rolled up into this one, "DNT" header. If you use Firefox 4.0b11 or later, you don't need this add-on anymore!