Trying out Firefox 4

Our new themes require we implement platform-specific changes. These can involve drawing in the title bar, for example, which you can't do in a cross-platform way. There are also the platform-specific styles that you either have to be able to query from the platform (GTK, for example) or build yourself.

In short, omplementing our UI in XUL and CSS means we only have to have one frontend (in a lot of cases), but the backend needs to be written too.

Hardware acceleration has nothing to do with this.