You might think to yourself that a discussion about web browsers has no place in website planning. You are very wrong in many ways. When planning your website or a website for a client you should keep in mind the user experience. After all the work is done, the user is going to use a web browser to visit your website. This is not a discussion or argument in favor of one browser or another. This is just a note about the market to which you are targeting your website. Over the past 4 years, mobile internet has became more popular than expected. We will dived this discussion to 2 separate ones.
Desktop and Laptops
Looking at the market share data on the right we can see the Internet Explorer still controllers 52% of the browser market share use. This should come as no surprise, because every new windows pc is shipped with Internet Explorer pre-installed. These figure are decaying, but it is not going to change by much in the near future. When you are planning a website, for yourself or a client, think about the browsers your average user might use. You may conclude that all your users will use Firefox, maybe because your website is about Firefox plugins. A good practice would be to test out the final product on the 4 major browsers, Explorer, Firefox, Chrome and Safari. If it works on all of these, chances are it will work on all.
The rise of the mobile internet almost duplicated any work web developer need to do. The data shows that currently (January 2012) Safari controls slightly over 52% of the market, with Opera mini and android trailing behind. This is a complete different ball game than what we saw in desktops and laptops browsers. Also, the screen size and functionality changed significantly with touch screens and smaller screen sizes. You should presume your users will want to access any website from a mobile device or a tablet and accommodate it accordingly. Sometimes that mean redoing the entire site and others just a minor CSS change. Either way, get hold of the main 3 devices or emulators and test out the final project on all browsers and platforms.
As a final note on browsers. This might seem like a lot of work, and sometime it is. However, after doing it once or twice without the initial thought, you will learn to keep all this in the back of your head even before you begin to think about development. As is with security, the end user has to be thought about throughout the entire process of building a website. At the end of the day, if you build a website users don't like, it's life will be very short lived.