This translate extension seems the most natural for just translating the web page you're on, a bit like Chrome's. It stays out of the way until you need it and when it does translate, it does it in-place on the page you're looking at. It can also use Google's translate service, which is good.

I did find that I needed to turn off the feature where it shows a translate icon whenever you select some text, as that was a bit intrusive/distracting. It does have a good settings page.=