Mozilla has recently had a lot of blowback about several recent changes they’ve made to Firefox. They have introduced a Terms of Service and have updated their privacy policy to include vague language about data collection. I won’t go into detail here though, so if you don’t know what’s going on, this is a great summary:
As a reaction to this video, however, Ryan Sipes, a member of the Thunderbird team, went on video to clarify what the situation is. This video is definitely worth watching if you are interested in what is going on: