It's all credibly slick and cool. Just select About Firefox in the Help Menu which tells you your channel and click Change to select a new channel. You select your new channel and click on Apply and Update and Firefox installs a new version of itself and restarts.
But I have to wonder if this is the right approach for Firefox. As slick as Firefox's channel switcher is, I prefer Chrome's approach of having separate installs of the browser for different channels. With Chrome's Canary Build, you can have your cake and eat it too. One safe, always up to date browser and another separate browser with cutting edge, experimental technology which will occasionally crash. And one can have dozens of pages open in tabs and another can open to just one or to your start page.
Aurora on the by contrast feels like an all or nothing proposition. You can switch between channels easily within one install of the browser but what happens if the latest nightly Aurora build is unstable? Will there be a way to switch to a more stable channel without bringing up the About Firefox box? I hope so.
And I think that Firefox with its more powerful extensions can benefit even more by having two separate browser installations. It is fairly common for early Betas of Firefox to be incompatible with many extensions. Having a "stable" installation of Firefox with all your favorite extensions and a second "experimental" installation which runs alongside it would probably be something that most Firefox users would enjoy.
While I realize that I could probably set this up myself using Firefox's Profile Manager, that tool is on its way out. And in any case it's probably overkill for most users. It would be much easier to have a check box that says "Maintain Separate Aurora Installation" or something like that in the About Firefox box.