add-on-->"extension (?)" Add-on is a term used by most browsers that includes both plug-ins (such as Flash, QuickTime, Adobe Reader, etc. that are included in

add-on-->"extension (?)" Add-on is a term used by most browsers that includes both plug-ins (such as Flash, QuickTime, Adobe Reader, etc. that are included in a webpage via object or embed tags) and extensions (Adblock Plus, FlashBlock, Ghostery, etc. which alter the UI and/or inject JavaScript). The term doesn't seem exactly right here, though, since I don't think Google uses the term at all for Chrome. Edit: Originally was going to write that it was a Firefox term (at least with respect to browsers), but wanted to publish and hoped I could research the other browsers before someone responded. After a little more searching it seems like Opera uses the term add-on (http://www.opera.com/addons/ http://www.opera.com/addons/) as well, although I don't think it includes plug-ins. Regardless, the use of the term in most cases is likely due to Firefox.