Working for me in Thunderbird 45 Rated 5 out of 5 stars

I'm on a Windows machine. On versions 38 and below, the utility RBTray (available on SourceForge) worked to minimize Thunderbird to the tray. With the upgrade to version 45 it stopped.

MinimizeToTray works with Thunderbird 45. After you install the Add-on, go to its options. In Minimize to tray, I have 'When minimizing' selected. When I minimize Thunderbird, it properly goes down to the system tray.

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Excelente y sencillo en Win8 Rated 5 out of 5 stars

Funciona de maravilla y así desocupo espacio en mi barra de tareas y mando a trabajar en segundo plano a Thunderbird a Área de notificación.

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Отлично Rated 5 out of 5 stars

Мне нравится, хорошая вешь.

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Works fine and cool [Win10] [TB v38.5.1] Rated 5 out of 5 stars

Yes it works.. but you have to activate it from options because after installation default options does not change the default behavior of TB.
Add-ons manager (or Tools add-ons) -- > Extensions -- > select options of this extensions and change the behavior you want.
I chose "Instead of closing and minimizing"

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Clever! Rated 4 out of 5 stars

I keep a minimized FF on tray at all times, immenediately after windows log in. It makes loading a (second) session/window whnen I need it so much faster! Faster than chrome that is! ;)

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Wonderful Rated 5 out of 5 stars

Really makes the tray more useful!

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

great! Rated 5 out of 5 stars

とてもいいです!
40.0.3

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Only works on minimize, not on close Rated 4 out of 5 stars

Tried on Fx 42 beta, Linux, XCFE 4.12 (Debian).
Closing Firefox doesn't minimize, but closes the program.

Thanks

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Rated 1 out of 5 stars

Does not work for Thunderbird 38.2.0 under Mint, so probably same problem in Ubuntu 14.04

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Rated 5 out of 5 stars

В последних версиях Thunderbird перестало сворачивать с кнопки "В трей" (2015.08.30)

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Still the best. Rated 5 out of 5 stars

Simple but effective without bothering me with stuff I don't need or want, sometimes no updates for years are a good thing (as long as it stays compatible).

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Gefällt mir sehr Rated 5 out of 5 stars

Hallo,
tolle Erweiterung für Thunderbird. Ich nutze es in TB Version 38.1.0. auf Windows 10. Läuft bei mir fast ohne Probleme. Nur das Minimieren über den Addon-Button funktioniert nicht. Aber damit kann ich leben. Cool wäre, wenn man den Button ohne Text oben unter dem Minimieren-Schaltfläche (vom Fenster) einfügen könnte.
Ansonsten eine tolle Arbeit, die der Entwickler hier gemacht hat.

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Problems in Thunderbird 38.1 Rated 4 out of 5 stars

It's not working properly in TB 38.1.
Please update the addon.

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Does'nt work in TB38.1.0... Rated 3 out of 5 stars

... but in FF 39.0 works fine

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

missing the 'write new mail' command in right-click menu Rated 4 out of 5 stars

adds an important feature to tb. I'm using it since many years, it works now in 31.8.0 esr. But in the past there was a 'write new mail' command in the right-click menu that I'm really missing now. An other issue: when you have a second tb window accidentally you cannot close it permanently without deactivating this addon.

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Actually it does partially work on TB 38.1 Rated 3 out of 5 stars

At least the WINNT-64 and the Linux-64 versions do mostly work, only the F9 command is not working, neither from the menu nor from the keyboard.

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

not work in 38.0.1 Rated 5 out of 5 stars

not work in 38.0.1

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Rated 4 out of 5 stars

don't work with tb38

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

Rated 3 out of 5 stars

It's a good idea, but causes the program to start two (or even three) instances at the same time.

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed). 

to tray Rated 5 out of 5 stars

Please fix one of the best addons for thunderbird

This review is for a previous version of the add-on (1.1.2.1-signed.1-signed).