Mozilla takes donations, so it isn't necessarely free. Also Mozilla is wondering why no one wants to use their software, this is one of the reasons why.
>Mozilla takes donations, so it isn't necessarely free.
This is a wild take. Taking donations doesn't invalidate the fact that it is available to everyone for free. By definition donations are voluntary. No part of Thunderbird is behind paywalls of any sort.
Hard to know! Composing emails in tabs seemed easy without internal knowledge, but the code turned out to be a trainwreck, to the point that even a funded attempt failed. I doubt it will ever be fixed.