The toolbar menu is inconsistent: 'Get Messages' is represented by a cloud icon, while 'New Message' is presented as text. This change occurred after an upgrade, and I hope that upcoming upgrades will revert to the previous toolbar style.
It has now been over two years since the request was made to change the ‘Get new messages’ button. We wonder what Mozilla is waiting for to fix this issue! It seems insurmountable! It's a bit like the issue with the completely useless two-letter icons in Thunderbird for mobiles (e.g. K9). On the other hand, we often receive calls for donations!
Simply for information purposes https://www.youtube.com/embed/pzJUpozQDwM You can also create a message, Check for new messages, in the draft folder. And with new window, Check for new messages.