On the Mac, Contribute uses the same (system-level) rendering engine as Safari, which means you should not get any nasty surprises with the layout.
Are you sure? Some time ago there was a deal between Macromedia and Opera: http://www.opera.com/pressreleases/en/2002/07/20020702.dml (oh, and Apple: http://www.macminute.com/2003/09/30/opera)
Test it: body {content: "It's Opera";}
-- regards, Kornel Lesiński
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