I have FF v21 for Windows but I don't see the updates to the UI. For instance, my tabs are still under my bookmark toolbar, I don't see the Firefox button in the top left and I don't see the bookmark button on the right. I'm using an add-on theme but tried setting it to the default to see if that made a difference...it didn't.
This is because you are on Windows XP. Firefox doesn't switch XP users over to the new UI on an update. You can turn it on however if you'd like. Go to View, then Toolbars, then uncheck the Menu Bar. You should see the Firefox button now.