Mozilla has allowed the AVG and Avast Online Security extensions back into their addons site. The extensions check if an URL the user is visiting is a malicious, phishing, or a scam site and warn the user. Mozilla removed the extensions in December after it was discovered that they were sending a large amount of user tracking data to Avast’s and AVG’s servers. Avast said they were making changes to the extensions to meet Mozilla’s requirements and that they would be available again when finished.
Source: https://www.bleepingcomputer.com/news/security/avast-and-avg-firefox-extensions-added-back-to-mozilla-addons-site/