Read the full article hereIf you search for Avast or AVG on the official Mozilla Add-ons website, you may notice that no results by these companies are returned. Neither Avast Online Security or SafePrice, nor AVG Online Security or SafePrice, are returned by the Store currently even though these extensions exist.
It appears that Mozilla removed these extensions from its Store. When you try to open one of the Store URLs of Avast or AVG extensions you get a "Oops! We can't find that page" error message.
Wladimir Palant, creator of AdBlock Plus, published an analysis of Avast extensions in late October 2018 on his personal site. He discovered that Avast's extension transmitted data to Avast that provided Avast with browsing history information. The data that the extension submits exceeded what is necessary to function according to Palant.
The extensions include the full address of the page, the page title, referer, and other data in the request. Data is submitted when pages are opened but also when tabs are switched. On search pages, every single link on the page is submitted as well.