Any modern Mac browser that supports JavaScript can use our "plaintext editor" mode.

As for the richtext editor, Mozilla on the Mac actually supports the features we need to make richtext editing work!  Please see

Can I use the premium xTools editor in Mozilla, Opera, or other alternative browsers?
http://help.xanga.com/premiumrichtextxtoolsalternative.htm

We'd like to support other Mac browsers, but none of the Mac browsers out there have the technology we need to support it - not even Safari!  The older browsers (like Internet Explorer for the Mac) are really out of date, because Microsoft has stopped releasing browsers for the Mac (surprise!) and the last version was released 3 years ago.

We've done what we can with Mac IE and Safari browsers.  For example, we've built in support for our picture upload feature into all Mac browsers!  You can post pictures into the Mac editor by clicking the PIC button.