Websites open with big displays, (apparent) low resolution

My display resolution is 1280 X 768 and the desktop looks fine, When I log on to (for example Hotmail, Yahoo, others), the image on the screen looks like a 640×480, In other words, the website more than fills the screen and the type looks like 24 point or more (can’t really tell). In short it is magnified. Changing resolution doesn’t help, chkdsk finds nothing wrong. Looking for a solution. Thank you anybody. (Will do a virus scan and a spyware as well while I ponder this).
Jim