It is not really enough to just compare looks. For example, even Amazon sites on Firefox 3.6.* browsers in the last couple of months show extremely inconsisten

It is not really enough to just compare looks. For example, even Amazon sites on Firefox 3.6.* browsers in the last couple of months show extremely inconsistent behaviour, e.g. inability to submit new searches after an existing search. I suspect the only sites that actually work on that list without significant issues are Google and Wikipedia, both optimized to be highly compatible.