Someone is busy trying to make people uneasy about Mozilla Thunderbird and Firefox.
This smells like a smear campaign, and sadly enough, the feddiverse is buying into it - big time!
I don’t mind giving Mozilla some telemetry, because I actually have no reason to believe, that they are not anonymizing it, and that they use it to do anything else than make their product better for us. Can anyone show anything else? No, they can’t…
This is probably paid propaganda, from someone who wants you to leave Mozilla - the prime organisation that fights for internet users rights and privacy.
Well, Mozilla makes contact to pages because it checks for your calendar, your mail, updates to your addons, updates to the browser/mail client, sends anonymous telemetry, that helps them make the software better, and doesn’t compromise you in any way. If you have addons installed, they might contact different sites to update blocking lists, change settings to bypass some youtube setting and so forth.
Get informed, and not by haters here, don’t panic!
Any decent software developer would like to see how their software is used, to make it even better. I guess your reason here is, that since they want to make their software better, you should not use it!? It doesn’t make sense, unless you are deeply paranoid.