I want to share a couple of updater-related things with everyone:
1) There is a minor user experience change in ESR31-based browsers: an update check is performed as soon as the about dialog is opened (there is no longer a need to click a "Check for Update" button). I think this is OK. With the preference settings that we ship with, users will then be told if an update is available and then they will need to click a button to download and install it.
2) Once someone is on a particular update channel, they will stay on that channel unless they download a new browser package (outside of the update process) that is built for a different channel. We could modify code to change this behavior, but it is what Mozilla does and I think it makes sense (MAR file generation skips the files defaults/prefs/channel-prefs.js and update-settings.ini). This means that when we release 4.0 (which will be on the "release" update channel) we could, if we want to, also upgrade alpha users to that same set of builds. Then, as soon as we deliver a new alpha release, we can upgrade only those users who were and remain on the alpha channel to the new alpha.