Hello there We have read the message We try to help

https://support.mozilla.org/en-US/kb/unified-toolbar

Your submit button has disappeared according to your writing, okay. We've had a new look for a while now and some buttons have been moved.

If you wanted to use your submit button and replace it as it is, you could drag it from a palette where all the buttons are located and I'll show you the way here.

I am also sending you a form containing this explanation for versions of Thunderbird software from the time Supernova was created.

Greetings Firefox volunteer

Please restrict yourself to the original posting on the topic where David was trying to help you. https://support.mozilla.org/en-US/questions/1438918