The extension is being installed with Avast Antivirus but you can also install and using it without antivirus.
Chrome: https://chrome.google.com/webstore/detail/avast-online-security/gomekmidlodglbbmalcneegieacbdmki?hl=en
Firefox: https://addons.mozilla.org/en-US/firefox/addon/avast-online-security/
Opera: https://addons.opera.com/en/extensions/details/avast-online-security/
Edge: coming soon
Safari: coming later