What does HackerNews think of birdtray?
new mail system tray notification icon for Thunderbird
Birdtray [1] works perfectly for this. I think the only thing you have to is create a .desktop file that opens birdtray that opens Thunderbird automatically.
> Inability to easily edit the from address
There is a feature for this for quite a while. In the write message window, just click the down arrow next to 'From' and either choose a pre-configured identity [2] or click "Customize From Address" which allows you to freely edit the from address.
> And TB still doesn't "remember" which -from- addresses are used by which -to- address.
Not sure what you mean, but there is a 'Reply from this identity when delivery headers match' config in account settings. I have never used it, but it allows you to automatically choose an identity when you are replying to a email from a particular address/domain.
[1] https://github.com/gyunaev/birdtray
[2] You can add many identities for each server in account settings.
It's made to replace the old firetray extension.