Branching and maintenance strategy, tracking mozilla releases, notifying users?

Now that this is at least minimally working, one consideration is how to handle evolving changes to Mozilla which could break builds here.

In particular, [Mozilla Firefox's release calendar](https://wiki.mozilla.org/Release_Management/Calendar) shows:
- extended-support release branches are good for a little over a year,
- general releases are good for four weeks,
- mozilla-central is a moving target.

I don't know how to approach this yet.