“Part of WCM is accessibility. SharePoint 2007 is for the most part jailed to Internet Explorer. Sure, you can load any SharePoint site in Firefox or Chrome, but it’s not fully supported and several features do not function correctly.
Firefox now has roughly 25% of the browser market share, and Microsoft is listening. In 2010, Firefox 3 is now a tier 1 supported browser. This essentially means that it has the same level of support as IE, but only on Windows machines.
Although you might not have the same experience on Mac or Linux with Firefox, Safari 3 is now a tier 2 supported browser. That will no doubt increase the ability of non-Windows users to browse SharePoint sites in an environment they are comfortable with.”