FireFox 1.5 is nice, but it has a very serious problem for me.
It doesn't support Hebrew well. It can display it, but it doesn't support mixing it with English or with numbers.
Here is how a page looks like in FireFox 1.5:
Here is how it looks like in IE 6: (This is correct).
I once had to implement printing a mixed document of Hebrew, English and numbers. The amount of stuff that you need to do it is staggering. And you are never going to get it truly right.
It's interesting to note that FireFox 1.0 did support it.