Most websites hard-code the dimensions and layout of their webpages so that it looks just a certain way. They may support multiple monitor sizes/resolutions, but if yours isn't expressly supported you'll either end up having to scroll side to side or staring at white space. You can create a custom CSS, which is something I have done for the websites I visit most frequently, but you have to do it for each individual site after analyzing some of the site's code. Thus, it's limited and not for everyone.
P.S. If you do decide to look into adding a custom CSS, note its abilities to omit content as well, such as sponsored advertising.
Is there a way to set your browser to fit in a 16:9 format for wide screen monitors b/c, for example, when I go to the yahoo page, there is a lot of empty space on the right and left sides?
Any fix for this?