Telemetry from bug 952543, combined with other AddonManager telemetry, is showing roughly 0.1% of Nightly sessions where AddonManager.startup() runs to completion, but XPIProvider.startup() does not log its timestamps. There is a preference, "extensions.defaultProviders.enabled", which could be causing this but I'd be surprised if 0.1% of profiles had that set. Aside from that there's very little code that could fail between where we record AMI_startup_begin and XPI_startup_begin *without* logging an exception. I think the next step is to record extensions.defaultProviders.enabled in telemetry and cover the gaps where we could skip XPI_startup_begin without reporting a failure.
Created attachment 8400344 [details] [diff] [review] Record default providers pref and a few more possible exceptions in Telemetry
https://hg.mozilla.org/integration/fx-team/rev/bc716fe4c06d Should this be leave-open?