The logistics of the update are being discussed in https://groups.google.com/forum/#!topic/mozilla.dev.planning..., with the current proposal available at https://wiki.mozilla.org/MPL_Upgrade.

One idea is to update the codebase at the beginning of the cycle that will end up being released as Firefox 13.

Right now.

Bug 715549[1] tracks the process of updating the boilerplate contained in files across the project from the MPL 1.1 boilerplate to MPL 2.0. But you don't have to wait for that to happen before you can begin using the code[2] under the new license.

The MPL is forward-compatible with future versions of the license.[3] (Section 6 says "Netscape", but this is one of the rights the Mozilla Foundation obtained from AOL.)

1. https://bugzilla.mozilla.org/show_bug.cgi?id=715549

2. MPL-licensed code, of course

3. http://www.mozilla.org/MPL/1.1/#section-6

The codebase will be updated soonish, so I'd expect this to be for Firefox 12.