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AFAIK, only the HTMLArea wysiwyg editor works on a Mac and that's only in OSX and only in Firefox. If you're thinking, "that's bad seeing the Mac is supposed to be so cool"... you would be absolutely right!
If you don't have a choice of editor in Tiny Content (sorry, but I don't use it) then you have a problem. However, your Mac fan has a problem anyway, because they will not be able to use a wysiwyg editor on *any* CMS, unless it uses HTMLArea and they edit it in Firefox.
If you design sites for a living I recommend getting a Mac to test things in Mac browsers, even if you only use it for that one task. Any old Mac that will run OSX will do. Conversely, your Mac-user clients will have to accept that they may need to get a cheap PC to edit their CMS website, even if they only use it for that one task. The rest of the time they can keep it in a cupboard!