This is excellent news; it was managable but tough to use natwest previously (fake user agent string + feature loss on site) but now it works just as well as in IE. It's also great news because once a few sites start doing this it gives credance to Mozilla and the idea of actually coding to standards.
"Stuart wrote in to tell us that the UK bank NatWest have recently upgraded their online banking facilities, allowing Mozilla users to access the service for the first time. In addition, the digital banking features of NatWest's parent, The Royal Bank of Scotland, are also now compatible with Mozilla. See bug 66911 and bug 119134 for details."