That message "managed by your organization" has nothing to do with any extension. In fact, I reiterate that you do not need to use any extension in Avast/AVG as the web/phishing protection works just fine without it.
That message in Firefox and Chrome (as well as all other browsers that the Avast/AVG can detect) is down to the product forcing these browsers to use certain settings and security certificates the Avast/AVG products installs on the system. Mainly to change QUIC traffic to HTTP/2, because Avast's web shield doesn't scan QUIC yet as it is an experimental protocol. Since the user cannot be bothered to change settings on his browser, Avast decided to "impose" the settings. That's where this "managed by your organization" comes from. Avast/AVG also apparently is able to inject new browser tabs with ads for their SafePrice and Online Security extension, as has happened to me a couple of times (usually immediately after installation).