Not really. I wish the Mozilla Foundation would rejuvenate their email client once and for all.
I found Nylas N1[0] works well, it's cross platform which is a big plus and has plenty of kb shortcuts.
[0]: https://nylas.com/
AFAIK Nylas doesn't work locally, but through their "cloud APIs". They are not alone in doing this, for example Outlook for Android does it too.
That's not acceptable for me. The email client should only communicate with the email provider. Trusting Google or Fastmail with my email is a leap of faith on its own without an extra third party involved.
I'd also question their business model. If Nylas Mail syncs via their own "cloud", it means it's not free to operate on an ongoing basis, which means it will end up either milking users for ads or die.
I would love that too. Sometime last year Mozilla enabled donating specifically to the Thunderbird project (which was a long time wish of mine) as opposed to donating to Mozilla as one entity, and I started donating to it. With more monetary support, we could have possibly have it become much better again (native and good Exchange calendaring support without extensions would be my top wish - the current scheme with the integrated Lightning and Exchange Provider is quite buggy).