https://www.bleepingcomputer.com/news/software/avast-and-avg-firefox-extensions-pulled-from-mozilla-addons-site/

Mozilla has removed four extensions from Avast and AVG from the Firefox addon site over concerns that they were tracking a user's activity as they are browsed the web.

When Avast and AVG antivirus is installed, the software will also install their respective Firefox and Chrome extensions named Avast Online Security, AVG Online Security, Avast SafePrice, and AVG SafePrice.