The content of the article does not really make a technical argument. It just says "XUL can not be fast, because I said so". The code of Firefox has always been

The content of the article does not really make a technical argument. It just says "XUL can not be fast, because I said so". The code of Firefox has always been a historical grown mess with a lot of loose ends that need to be entangled. I'm convinced that a XUL version can be made fast as well if you spend the appropriate amount of engineering hours on it.