Although most people will stick with a favorite browser to view web sites there are a multitude to chose from … Safari, Internet Explorer, Netscape, Mozilla Firefox …. and all of these have many versions
Consider browser choice with operating systems( e.g Linux Fedora Core 4, Macintosh OSX 10.4, Windows 98, Windows XP) and the different combinations grows horribly large.
As a web designer an important consideration in designing and coding a web site is how well it is going to perform across the gamut of browser and operation systems. In an ideal world all browsers would display any given web site in exactly the same way. Alas this is not the case. What may perform fabulously on Internet Explorer 6.0 may be full of flaws when viewed using Netscape 7.2.
During the development of our web sites we constantly test our code to see how it performs… testing them on a total of 53 browser/operating system combinations. This enables us to tweak our code so our web sites look good and perform as designed no matter what operating system or browser you or your site visitors are using.