Well to be honest what I can't see is why any browser is not displaying it like chrome. In my view chrome tends to be the most accurate renderer.

I mean the <li> are inline so why is there a line break happening at all? Validation does not really have much to do with it. The html is valid but the way that the two browsers are rendering it is different. My point is that actually I think that the way chrome is rendering it seems most accurate. I can't see why the <li> would be on different rows. ( but I have only glanced at it so may be missing something)

Anyway, that is all a bit moot. Change to block and it will all start to work or at least you'll see why it doesn't.