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What plug-ins might be recommended for Mac OS X and Firefox?>
What other applications might be good for the Mac?Those are more or less rhetorical questions; you'll get useful results only if you tell us what functionality you desire and can't find.
Edit: Personally, I've found all of my 3rd party apps and Safari extensions by perusing
MacUpdate: Download Apple Mac Software daily and reading FTM and MFIF posts.
Edit 2: Have you noticed that the cat in your avatar freezes periodically?