This collects client-side fxa-content-server data. The data covers
only the about:accounts experience until:
* the fxa-content-server provides the LOADED message; or
* connection failure is observed.
Nota bene: a healthy fxa-content-server always delivers the LOADED
message! In future, we might want to timeout the load (and observe
said timeouts) separately.
We collect no data after the fxa-content-server LOADED message. The
intention is for the server-side metrics flow to capture the valuable
"bounce rate" metrics, since the fxa-content-server team are in
position to quickly improve the web-based UI flow.
The client-side data collected is intended to answer the following
questions:
1) How many remote content loads started;
2) How many loads completed;
3) What proportion of loads made it to the LOADED message, as opposed
to failed;
4) How long it took each successful load to observe the LOADED
message;
5) How long it took each failing load to observe failure.
All of these are keyed by the fxa-content-server endpoint path (like
'settings' or 'profile/avatar'), since I observe differences between
the time-to-LOADED for each endpoint path.
There is a privacy trade-off here. Mozilla is collecting data to
understand the user experience when about:accounts is connecting to
the specific fxa-content-server hosted by Mozilla at
accounts.firefox.com. However, we don't want to observe what
alternate servers users might be using, so we can't collect the whole
URL. Here, we filter the data based on whether the user is /not/
using accounts.firefox.com, and then record just the endpoint path.
Other collected data could expose that the user is using Firefox
Accounts, and together, that leaks the number of users not using
accounts.firefox.com. We accept this leak: Mozilla already collects
data about whether Sync (both legacy and FxA) is using a custom server
in various situations: see the WEAVE_CUSTOM_* Telemetry histograms.
By making the updated system add-on install location return an empty set when
in safe mode it causes us to rescan and enable the default system add-ons.
The complication is calling the uninstall method on the updated add-ons when
switching to safe mode, for that we have to cache the fact that an add-on
can run in safe mode in the bootstrappedAddons data so it persists to the
next restart and can be accessed when the updated add-on has been hidden.
