When running addon it has this statement as part of privacy policy:

"If you choose not to allow us to collect anonymous data, the FDM extension will be immediately removed from your browser."

This is not present on the privacy policy shared on firefox addon store.

The main issue is deception, but using such underhanded tactics is not great either. They never disclose what data will be collected or anonymized either.

Edit: found this response "We've implemented the recent anonymous data usage notification only to comply with the latest Mozilla’s requirements."

On one hand it is clearly stated that anonymous data is collected, on the other, this response implies that this is only because mozila required this statement. The only conclusion I can reach is that mozila is asking all addons to add this note no mater if they are collecting data or not, which, while possible, is hard to believe.

Edit 2: Some other comments from developers imply that this is to allow downloads (i.e. you need to send URL to server to download, etc). But all this is already called out separately and in great details outside of this mysterious anonymous telemetry. Thus, this is just necessary.