Firefox Desktop Telemetry Use Counter Probes are no more

[Chris H-C]

Starting with Firefox Desktop Nightly 124 build 20240202094312, uplift pending to Firefox Beta 123.0b7, Telemetry no longer reports Use Counter probes[1]. You will find equivalent data in the Glean "use-counters" ping[2].

Background:
Use Counters[3] are counts of the use of various features of the web platform. Mozilla needs to know how often, for example, CSS properties are used across the web in order to prioritize work and understand when deprecated features can be removed. To report these use counters to Mozilla, we employ a data collection system.

Previously, this data collection system was Telemetry. In Firefox 121 we added use counter reporting via Glean. And now, after validation[4], we've removed the Telemetry parts.

Why:
We have a lot of use counters (2309 as of time of writing[5]). Telemetry was sending them as Histograms which are a very inefficient way to report counts. By switching to Glean we have decreased the size of sending each use counter by 75%.

(Due to compression, ping structure and scheduling, and that switching to Glean finally enabled worker-type use counters to be reported, this results in average data storage savings of 60%.)

Also, by using Glean, use counters can be (and, as of Firefox 121, are) reported in all Mozilla projects that use Gecko and Glean, notably Firefox for Android[6] and Firefox Focus[7] and Klar[8] for Android. If we are able to pursue Gecko on iOS, they'll be reported from there as well.

Anything else:
We have released a public use counters dataset for both Firefox Desktop and Firefox for Android[9]. Please use it and tell us what you think.

The venerable Use Counter Dashboard[10] remains frozen with information only up to December 19 (part of the Measurements Dashboard deprecation[11]). We intend to furnish it with Glean-reported data in DENG-2547[12].

Questions:

  If you have any questions, please do ask them of us on Matrix in #glean:mozilla.org or on Slack in #data-help.

Thank you for your attention,

:chutten and Emilio

[1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1877273
[2]: https://dictionary.telemetry.mozilla.org/apps/firefox_desktop/pings/use-counters
[3]: https://firefox-source-docs.mozilla.org/dom/use-counters.html
[4]: https://bugzilla.mozilla.org/show_bug.cgi?id=1874439
[5]: https://searchfox.org/mozilla-central/rev/34ba7989ae53b9112d543ce39d350b79dc2a16b4/dom/base/use_counter_metrics.yaml#134
[6]: https://dictionary.telemetry.mozilla.org/apps/fenix/pings/use-counters
[7]: https://dictionary.telemetry.mozilla.org/apps/focus_android/pings/use-counters
[8]: https://dictionary.telemetry.mozilla.org/apps/klar_android/pings/use-counters
[9]: https://public-data.telemetry.mozilla.org/all-datasets.json

[10]: https://mozilla.github.io/usecounters/

[11]: https://docs.google.com/document/d/1kqoiKTPzqE6Veqrjg77nsYRZChoR4OzKCJHDEppyDps/edit

[12]: https://mozilla-hub.atlassian.net/browse/DENG-2547