I just scanned and the Downloader.IstBar.ja is gone. However, I still am encountering "adware tracking cookies" each time.
Tracking cookies are a waste of time and effort even bothering with (I disable this option in the SAS Preferences), they aren't a security issue, but if anything a minor privacy issue. Many sites place cookies and most would be classed as tracking as they retain details about your activity (on the site that set the cookie). The don't gather information on other sites you visit and other sites can't access the cookies of other sites.
I never allow third party cookies, ones set by other than the site you are visiting, but you may find it difficult browsing some sites if you block cookies completely. Firefox and other browsers should allow for the blocking of third party cookies. You should however, periodically clear out your browser cache (temp internet files), internet history and cookies, etc.