Website browser compatibility or cross-browser rendering (which is a more accurate term) is a problem that has plagued website developers since the beginning of time, or 1994. 1994 being the year in which Netscape Navigator was launched, where it basked in its glory until 1995, and then the great Browser War started with the release of Internet Explorer. This lasted until the dawn of the new millennium, and during those dark times it was common for web designers to display “best viewed in Netscape” or “best viewed in Internet Explorer” logos. Websites could look perfect in one browser and be barely readable in another.
Even though Microsoft won that war, browser compatibility was still an issue as Internet Explorer did not follow the W3C Guidelines. So flash forward to 2008, and although Internet Explorer is still king, a strong following for Firefox and Safari means that you still have to be very careful when building a website to make sure it works well in all the major browsers.
For the most part, the resulting differences are a lot less noticeable from the dark days, and are mostly caused when correct formatting is not used and the browser fills in for what should be there. But care should still be taken to check that your site works well and is readable, if not the same, no matter what browser it’s displayed in.