Prism for Firefox is an upcoming powerful extension that lets you create stand-alone web apps directly from Firefox. These applications run in their own process and have there own separate memory. This feature has been presented in other browsers as well, like Google Chrome, but Prism gives more flexibility even though it is still in the labs.
This blog post is written on Google Docs with Prism, and I had a very smooth experience even though I had a lot of other applications running in the background. Prism gives you the option to hide all the browser GUI components or choose the one you like (I preferred to have the Status Bar visible) and you can even customize the icon of the application.
Prism applications maintain their own session and are not bounded to Firefox. So you can sign in as a different user in the same service at the same time. This is a huge advantage if you want to check two Gmail accounts at the same time. You can be logged in to both simultaneously.
The normal browser context menu also disappears leaving you with the pretty basic edit options (Cut/Copy/Paste etc). This however didn't appeal to me as I wanted to use Ubiquity here. But since this is at a early development stage, we can hope to see that extensions would find their way into Prism. Note that prism does present an option to install addons but there aren't any available at this time.
As always, I would love to hear your thoughts about this new extension, which is pretty much an application on its own right.