It has to do with the version of Gecko engine. I tried with 1.5.4 and 1.6.0a3 and there is a big difference. I saw the same style that you see with 1.5.4 version. With 1.6.0a3 it looks like Opera.
The alpha code KM 1.6.0a3 is so good that I am using it in almost every application. The only place I still use the 1.5.4 is my bank, and only because they will not allow alpha coded browers.