Usually, I'd use Adblock to magic it away, but the box is part of the page and can't be targeted by its address. So, let's use Firebug to take a look at the offending element...
The bit we want to hide is the "cN-flyIn" div, I'm going to use Stylish to hide it. Stylish is an add-on for Firefox and Chrome that lets you edit the CSS files that tell your web browser how to display web pages. As well as turning your Facebook pink, you can use it to move, resize and hide elements of your favourite websites.
After installing Stylish, click its little "S" icon and select "Write new style -> For smh.com.au"
Now, in the window that appears, paste this code:
@namespace url(http://www.w3.org/1999/xhtml);
@-moz-document domain("smh.com.au") {
.cN-flyIn {
display:none !important;
}
}
And that's it, the box is gone!