There is a setting in Thunderbird for the startup page. This is wonderful because I can basically use my favorite Firefox New Tab extension, like you see in the attached screenshots below.
The problem is that, I cannot close the message panel to get back to my favorite home page, and even worse, even if I did, the home page doesn't load back up. Instead, a blank black screen will be loaded.
I think adding this feature, from a software development perspective, is relatively cheap, but from a feature perspective, it is very eye catching!!