You may be interested in reading a previous discussion on this.
No Support for MacIntosh????
To summarize some of the discussion...
Firefox on the Mac: This is the browser we recommend to Mac users. The editor does work as intended on Firefox.
Safari on the Mac: The problem with Safari is that it
doesn't have the proper support for the rich editing surface the editor
requires. The next version of the forums, which is scheduled to
be released in Jan, should include an alternative editor for Safari
users.
IE on the Mac: Microsoft dropped support of
this browser back in 2002/2003 and said that they will not be
developing future versions of IE on the Mac. People should switch to Firefox or Safari if they can.