"Send Later Button" add-on doesn't seem to do anything

I’m trying to test Thunderbird’s “Send Later Button” add-on. It’s supposed to add a “Send Later” button to the Write window’s toolbar, but I don’t see that button appear. I’m on Windows 10 Pro, running Thunderbird 68.4.1 (64-bit). Thunderbird says it is “up to date”. Is that add-on working for other users?

https://addons.thunderbird.net/en-US/thunderbird/addon/send-later-button/
It works here, but you have to add it to the Write window’s Composition Toolbar by right-clicking the bar, Customize, and dragging the button onto the bar.

1 Like