Shoutbox

I recently got a new pc, and when I clicked on the mail button at the top of the contact list page of WLM, it opened my Windows Live Hotmail (WLH) inbox in a new tab in my current internet explorer window, or if i didn't have one open, opened internet explorer in a maximised window.  However, after a couple of weeks, when i click on the button on the CL page, it opens my WLH inbox in a new window of IE, and this window is not maximised - takes up only about a third of the screen.  Has anyone got any idea about how i can change it back so that it opens in a new tab, and are other people having the same problem?  Is there some setting somewhere that I need to change?

Thanks.

Information:
IE version: 7.0.6
OS: Windows Vista
WLM version: 8.1.0178