Your float is not cleared and it's margin is extending into your footer and moving your xxx over.
Try clearing the floats like this -
Removing the bottom margin also works -
margin: 10px 0 0;
Removing the bottom margin is just to show you what's going on. The correct way to fix this is to clear your floats.
Have a look at this page
that explains how overflow:auto; clears floats for you.