Thunderbird telemetry
Someone raised concerns here some time ago about Mozilla Thunderbird's collection of email domains during the setup process. Since then, things have clearly taken a turn for the worse. Thunderbird now operates an opt-out telemetry system, collecting all sorts of personal user data, ranging from IP to hardware specs. Details here: https://support.mozilla.org/en-US/kb/thunderbird-telemetry
Perhaps even more worrying is that Thunderbird shares user data with third parties (amazon.com, gandi.net, etc.) Details here: https://www.mozilla.org/en-US/privacy/thunderbird/
In my opinion, this is the very antithesis of what we're trying to remedy.