When you install the most recent version of avast! Free Antivirus, the company's avast! Online Security extension will be added to the browser (it is also added if you install a paid version).
Nowadays when you install a security suite, no matter if it is free or paid, it is likely that at least one browser extension is added by it during installation to popular web browsers such as Firefox, Internet Explorer or Google Chrome. By Martin Brinkmann on Main Firefox - Last Update: Febru18 comments
