When I'm clicking a link to start a download, sometimes the main window steals the focus from the download dialog. This is extremely annoying for me as I have a habit of pressing enter to get to the "save as" dialog. Instead, that key press will end up in the main window, and typically start a second download, since the download link is focused. This issue is present both on OSX and Windows, in FF 5.
Why does Firefox behave this way? Is this supposed to be a security feature? Is this change documented somewhere in any change log?
How can I turn it off?