Send is broken in every version after 38.7.2 (OSX 10.9.5)
In every version of Thunderbird after 38.7.2 (every released version tested up to 45.5.1), Send does not work. Clicking on the Send button does nothing and emails cannot be sent. If I revert to 38.7.2, Send works again.
(A side note: I had to use Safari to write this. Using Firefox, the Mozilla support "Ask this" button does not work! Unbelievable.)
Opaite Mbohovái (1)
Send does not work.
https://support.mozilla.org/kb/cannot-send-messages
Using Firefox, the Mozilla support "Ask this" button does not work!
My best guess is you're using some sort of security software/add-on and something gets blocked.