I've upgraded two PC's just last night to FF3 with one click.
I don't notice any changes to my personal settings (ie: download path) nor do I have any problems with stability. Seems fine.
I've also just done a fresh install (not an upgrade) on my new work laptop yesterday. Also good.

I hope you can resolve the problem easily, Doug! Perhaps install again?
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10101311 (20GB- backup empeg)
10101466 (2x60GB, Eutronix/GreenLights Blue) (Stolen!)