PSA: Data preference changes in Firefox 58

Georg Fritzsche gfritzsche at
Wed Nov 1 18:18:29 UTC 2017

*This a shorter summary; if you need more details see this blog post

As part of the Photon UI refresh, the Firefox data preferences were
streamlined. Previously we had two data controls for historic reasons, but

   - There is just one control for data upload for Firefox, which is on by
   - Individual measurements are now collected from either all users or
   prerelease users.

So for Firefox we now just differentiate between “release data” and
“prerelease data”. *(For some specific features or studies there may still
be explicit opt-in notifications, but this covers all standard Firefox data

As detailed in another post
this doesn’t change anything about the type of data being collected while
it makes the data controls less confusing. However, it does have some
technical consequences for Telemetry that we landed in Firefox 58.
What does this mean for me?

While this has broader technical impact on Firefox data collection, the
changes we landed should make this work mostly seamless.

For *Firefox users*, there is no significant change; the data upload
setting users chose is respected as before. The opt-in for additional
Telemetry data went away; instead we always collect less data on Firefox

For most *Firefox development*, nothing should change. Telemetry takes care
of doing the right thing for histograms, scalars & events internally.

Local builds from current mozilla-central should default to recording all
the prerelease data but not upload it, without any extra build flags.
*about:telemetry* allows you to confirm that.

For testing locally how release Telemetry behaves, there is a hidden pref:

For *Fennec development*, nothing changed. Fennec still has the same
Telemetry behavior and preference handling as before.

For *writing Firefox tests*, *nsITelemetry.canRecordExtended* can be used
to check whether prerelease data is recorded. The pref
*toolkit.telemetry.testing.overridePreRelease* can be used for tests that
need to enable prerelease behavior.

For *QAing Firefox data collection*, you might need to override the
prerelease status using the pref
*toolkit.telemetry.testing.overridePreRelease*. The prerelease and sending
status can be checked in *about:telemetry*.

If you are *looking at Telemetry data*, there are some changes. In Firefox
58, we will not receive the “extended” data from release anymore. This
directly affects some parts of that provided release
data from that small *“opt-in”* population:

   - the distribution and evolution dashboards will soon not show release
   data anymore.
   - telemetry.js
   and the aggregates service will not provide release data when 58 is

If you will be affected by these changes and need alternatives, please
reach out to us.
Reaching out

   - If you have any questions reach out
   to :gfritzsche, :chutten, :dexter, :frank or the team
   - For any specific issues, please file a bug
   We are using bug 1406390
   <> for tracking.
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