Here's how I read it... they're looking at ways to move towards rolling release for A/B testing.

Think about it like this, you're using Firefox and you get a notification... "Feature X is ready to test, would you like to try it out? Yes/No" If you select Yes, the feature is rolled out to you and other volunteers immediately (potentially without restarting, depending on the feature), and you can then feedback your experience to Mozilla on how well the new feature works out for you. The feedback from this control group then informs whether Feature X is ready for prime time.

In some ways it seems like it's a restructuring of the Firefox development channels, a mix of beta and stable releases in the same channel.