Tray implementations are actually on the horizon - recently taking shape with the help of community developers. For example Bug 2023000 - Implement Linux system tray: hide-to-tray
You may be confusing IMAP+js with pop+js. Pop is running as js, but the IMAP rewrite was abandoned early. IMAP will likely be rewritten in Rust in a future year.
Yes, FUD and long held myths can be found anywhere. But speaking as a staff member and someone who has seen first hand user reports, here is some straight shooting:
* there are rare cases of a profile either misplaced (exists but not correctly pointed to) or gone - it is something which I understand Firefox people are working on (Thunderbird uses the Firefox profile system)
* there are extremely rare reports where prefs.js is corrupted
* there are no compact failures in current versions - there are no open bug reports for recent versions, so it has been totally obliterated by a rewrite and subsequent fixes. Most user reports of compact failure are attributed to other causes of folder corruption
* folder corruption can occur as easily from external sources as from product bugs.
Also, beware drawing broad conclusions about other users' experience from one's own personal experience. I have almost never experienced corruption - once in the last 10 years. But I am also using a Thunderbird profile that has gone through 5 different laptops, two different OS, using daily builds, which is AMPLE opportunity to have had multiple catastrophic failures. But because I know other users experiences I consider myself lucky.
On the contrary, you ARE ALSO the target audience. It is stated so explicitly multiple times - for example "existing users will not be left behind", "you get to choose", etc.
> Mozilla started transitioning Thunderbird out of their umbrella while TB is still highly dependent on Firefox code.
If you are referring to Mozilla Messaging and the period to 2012, no the only transitioning was in terms of product functionality. The community organized in 2014, unaffiliated with Mozilla, and it's not until about 2018 when staff were hired that community leadership were able to seriously reduce technical debt. But seriously reducing dependency on Firefox code is some distance away.
> Maybe we need a successor to Thunderbird? Something that's not tied to Firefox so much?
You are looking a millions of dollars paid developer time.
> Because it seems like we can't trust Mozilla and however many unpaid/underpaid volunteers to maintain it well enough.
Mozilla are not running the show here, the community is.