Why doesn’t Mozilla make a Thunderbird add-on in Firefox with full e-mail functionality and a simple mail notification in header, when add-on is not in use (say an envelope animation, that tells you when to open add-on and check on mail. Well, the envelope would also be an actual add-on starter)? That would be nice… (Mabel 
Moved to the correct category.
Is there currently no notification when an email is received? If not there should be, this is critical, otherwise emails go overlooked and an addon to get this kind of functionality means the product is extremely lacking in standard functionality.