When you take into account the multitude of browsers there are now available on to web users today it's no wonder development of sites is taking longer. Firefox, Safari, Internet Explorer and Chrome are the 4 most used but are by no means an exhaustive list of available browsers.
A successful website has to work on all of these browsers as you just do not know what browser those all important visitors or customers will be using.
Here are the main issues that can occur when testing a website on different browsers:
Browser compatibility issues:
This is obviously the big issue with web design, well not so much with web designers but the browser manufacturers themselves. Why can not they all sing off the same hymn sheet and work together! Browser compatibility is tough to identify issues with and you rally do need to look at the site on a PC and a Mac. This is the sure fire way of confirming compatibility but there are tools to help you too.
Adobe BrowserLab (Google it for more info) allows you to see a fully rendered version of your site in multiple browsers and multiple versions as well. You'll see instantly where the site needs attention, if any, and it's probably the best tool to come onto the market for a long time.
Slow browser loading times:
You might find that your website runs like a steam train in say Firefox but when you look at it in Safari it takes an age to load up. Thankfully the web has provided us with a great little tools to check and identify what causes the problem. Both provided by the browsers in this case. YSlow is a Firefox extension that you can install on your browser and it will analyze your site and pick up any potential bottlenecks. If there are any you'll find once fixed your site should work fine on all browsers. Timeline that's built in to Google Chrome does something similar.
These two little gems will save you hours of digging around trying to fix niggly little problems with your site. If you really can not be bothered however to make your site cross-browser compatible then I'd suggest focusing on making it work in IE7 and Firefox. Firefox and IE8 are almost identical when it comes to rendering code so you've just eliminated the top 3 browsers used which are IE7, IE8 and Firefox on the PC.
Oh and shall we talk now about the mobile browsers like the iPad …
Guess that's another article waiting to be written.