Followup to bug 913899. > ::: toolkit/modules/AsyncShutdown.jsm > @@ +222,5 @@ > > + let msg = "A phase completion condition is" + > > + " taking too long to complete." + > > + " Condition: " + cond.name + > > + " Phase: " + topic; > > + warn(msg); > > I wish we could get telemetry (or some other kind of feedback) on this, but > it's likely to happen too late.

I believe that most clients will add blockers for profileBeforeChange, or ideally, even before this. Such clients can be recorded by Telemetry, since Telemetry can take into account everything up to profile-before-change, inclusive. I believe that we could use Telemetry to tell us, for each phase up to profileBeforeChange: 1. how many blockers we have; 2. how long we spend spinning the event loop; 3. which (if any) blockers trigger the timeout warning. Since 3. is more complicated, I believe that we can postpone it to a followup bug.