HTML hackers who think they are too clever to use the defaults often cause such problems. There is a forced setting that sets the screen to 100% of the display, there are also forced settings that set width in absolute pixel sizes. If I remember correctly the default will be 100% unless you start to physically set pixel numbers, but it's been a while, and it also depends on how like HTML 3.3 and V4 the current 'clever' versions are, and how much dicking around with 'HTML extensions' such as JS , Java, Flash, jsp, xyz, etc the hackers do...