No one uses Thunderbird anymore anyways, which doesn’t matter as the ToS changes to Firefox are a nothing burger and won’t dissuade millions of people using it daily despite what the neck beards on Lemmy would have you believe.

(e.g. you use Firefox to make a post, they have to process those keystrokes through Firefox to send it to the server, and thus could require permission to do that in the form of having a license)

A better example would be stored credentials, credit card information, and other PII type data.