Why does Ctrl-F4 mostly close a single document/tab in a multiple-document/tab interface (eg Firefox), but sometimes (eg if there’s only one doc/tab open, and the moon is full), it instead drops down dropdown boxes?

Alt-Down will also drop down a dropdown box. Which I guess is why back in Windows 3.1 the button to do the same looked like a down arrow underlined.

Oh yeah, and why, when using Alt-F4 to shutdown the Windows XP desktop, does it take two or three goes pressing it to get it to register? Like it doesn’t really believe me the first time?