During the holidays, I tried to study the Cascading Style Sheet (CSS) language using SAMS Teach Yourself: CSS in 24 Hours (2nd edition). One thing that has caught my attention was its topic on web browsers, as it is an essential Internet access tool. if the browser has been programmed to understand the style it has encountered, it will attempt to display it. If it has no idea what it has come across, it will ignore it or be confused. 

Base on my experience (supported by the theories that I've read), not all browser can run styled web-pages. And SAMS divided these web browsers into four (4) categories:

1. Ancient Browsers - are those that existed before CSS was even discovered. They ignore CSS rules entirely, giving your CSS-ran website a boring appearance. Some ancient browsers are:
   
   • Lynx (which is a text-only browser)
   • Mosaic (no longer in widespread use)
   • Netscape 3 (no longer in widespread use)
     
2. Broken Browser - is one that, when given a legitimate CSS rules, displays a mishmash of styles where information gets lost. The difference between an ancient browser and a broken browser is that ancient browsers don't try to display CSS, and broken browsers try and fail horribly.
   There are two approches to dealing with broken browsers. First, you can code around the problems by using a filter or other browser hack to prevent the browser from mangling your page. And second, for some browsers that are just so old that few people use them any more, you could just no longer support those browsers on your website.
   The list of broken browsers includes:
   
   • Internet Explorer 3 (no longer in widespread use)
   • Netscape 4 (no longer in widespread use)
3. Quirky Browsers - are generally compliant to CSS specifications but have serious problems that come out when you start doing complex styles-- for example, when using CSS to lay out a web page. If you are a web designer, you cannot just ignore them. The way to deal with these browsers is to understand their quirks and bugs and work around them. One strategy is to use only "safe" CSS code in your designs, even if that limits the effects you can produce in more compliant browsers. Another method for dealing with a quirky browser is to use filters and other browser hacks to tailor the style rules given to that browser.
   Some browsers with quirks include:
   
   • Internet Explorer 6, 5.5, and 5
   • Internet Explorer for Mac (no longer in widespread use)
   • Opera 5 & 6 (no longer in widespread use)
   • Netscape 6 (no longer in widespread use)
4. Compliant Browser - is one that follows the CSS and HTML specifications, that although, not 100% standard-compliant, they get very close, to the extent that they can be treated as basically compliant. Aside from the latest browsers, the following are generally compliant browsers:
   
   • Firefox 1.5 
   • iCab (alternative web browser for Mac)
   • Konqueror
     
   • Mozilla 1.7
   • Opera 8.5
     
   • Safari 1.3 and 2
     

To check if a browser is a compliant browser, Acid2 browser test could be used.

Internet Explorer is currently the most popular web browser but it is the least favorite current browser among designers who use CSS extensively. I have been an IE user for years already until a project has  pushed me to test my pages on Firefox. From then on, I never switched back to IE (only use it to test a CSS-ran page). As I have said before, I would stick to Firefox for now.

• Reference: SAMS Teach Yourself: CSS in 24 Hours (2nd edition)