I never have used this but a lot of people do it looks like.
A high-rated Firefox extension with more than 7 million downloads secretly collects data about every website the open-source browser visits and combines it with uniquely traceable information tied to the user, an independent security researcher said.
“The undisclosed behavior of the Ant Video Downloader and Player add-on takes place even when the Firefox private browsing mode is turned on or when users are availing themselves of anonymity services such as Tor. The add-on carries a rating of four out of five possible stars and gets an average of almost 7,000 downloads per day, according to official Mozilla statistics…”
Posted in ID, 20th May 2011