The browser is still in its infancy (it's an alpha release), and obviously only works on Windows, but the concept is rather interesting. You can switch rendering engines without restarting, and you can assign engines to specific websites. So, if your bank is still stuck in the middle ages, you can solve the issue by using Lunascape to browse with Gecko, but switch to Trident specifically when you launch your bank's website.
As said, the browser is far from done, which shows in slightly crude translations, lack of security features like SSL certificate details or phishing protection, but it's an interesting concept nonetheless. The release is freely available for download.