I use a pre intel emac, with OSX 10.4.9 and this works like a charm. Faster than Opera, zillions of times better than safari, and ultimately customisable in its appearance, you can probably tell that this is my preferred Browser.
If you are a serious eBayer, Mozilla's new, downloadable Firefox Companion for ebay is seamless and gives you a running sidebar of your latest bids and how they are performing.
Love it.