Hi -midnight,
I myself do not have the extension either. It is always good to know what battles are being fought over (y)our endangered privacy,
like with McAfee's SiteAdvisor. In 2004 it could not even been easily uninstalled from inside firefox (bug).
Especially as such extension services sometimes aren't allowed by law to call an (adware) spade an (adware) spade, because of a legal dispute. Sometimes adware posing as something complletely and utterly different can still hold a strong judiciary position, if they sue AV for flagging them as spyware/adware/riskware.
Expert in this field, Benjamin Edelman, has found this out early on in life:
http://www.benedelman.org/spyware/On such a dispute with Search7 read here:
http://www.theregister.co.uk/2008/08/28/7search_sues_mcafee/And also where McAfee's SiteAdvisor has become associated with certain Broadband Players (CDNs) as PlusNet for instance:
https://www.plus.net/help/archive/other/plusnet-protect-user-guide/So you see an adware related extension could rear it's ugly head from almost anywhere to help sell your data to third party vendors.
This is not only a threat to your privacy, but also means a threat to the overall security of all global users of the Interwebs.

your avast forum-friend,
polonus (volunteer website security analyst and website error-hunter)