Make calendar popup appear near mouse or below follow up button and on same monitor

[theperm]

this is important on multi montior setups, that the calendar appear on the same screen as thunderbird is on. Ideally is should appear just below the current mouse position or the center of thunderbird window no matterhow may screens there is. Currently it is appearing on the top left of my primary screen, which is no where near my thiunderbird window on another screen.