Firefox 7: Telemetry

Firefox 7 marks a turning point in how we measure Firefox performance. Traditionally we measured Firefox performance on individual developer machines and our build & release infrastructure. However it turns out synthetic benchmarks do not correspond to real-world Firefox usage: it is difficult to model a “typical” computer in a lab environment. Surprisingly slow consumer hardware, changes in usage patterns, preinstalled bloatware all affect Firefox performance in surprising ways.

Firefox 7 telemetry will prompt users to opt-in to reporting performance data to Mozilla. This data will supplement our existing benchmarking infrastructure to help us optimize future Firefox releases. Telemetry performance metrics are very lightweight and will not negatively impact Firefox performance.

In addition to transmitting data via SSL, Mozilla privacy team worked tirelessly to ensure that no personally-identifiable information is sent via telemetry. Whereas many other software projects stamp this kind of data with a unique per-user id, we opted for a per-session id which is reset every time the browser restarts. Telemetry is also disabled while in private-browsing mode.

The following telemetry data will be gathered in Firefox 7:

  • Memory usage
  • CPU core count
  • Cycle collection times
  • Startup speed

Use the about:telemetry extension to check on your browser performance. The following screenshot shows how to enable telemetry:

I’m very excited that Firefox finally joins the ranks of cars, airplanes and other software projects in making performance decisions based on real evidence gathered in the wild.



  1. Hello.

    Do you know if the addon about:telemetry will work fully in FF 6.0.2 if I force the compatibility with ACR addon?

    Or must I upgade to FF7?

  2. Okay, I just tested about:telemetry in FF6.0.2 with forced compatibility (by using ACR addon from Mozilla) and it works but partially.

    The line “Submit performance data” is missing in Options>Advanced but it can be enabled in about:config by changing toolkit.telemetry.enabled to true.

    The tab about:telemetry works but displays only a graph called nsCycleCollector::Collect.

    In Aurora, about:telemetry displays more graphs.

  3. Telemetry in FF6 is very barebone and unfinished. This is why we waited to enabled it in FF7. FF8 will be better yet :)

  4. Do you plan making telemetry data publicly available (a-la crash-stats)?

  5. @CAFxX,
    yes we plan to let extension developers add own probes and generally provide data to the public. However those pieces are not yet ready.

  6. Just upgraded to FF7, entered “about:telemetry” as URL -> “This URL is invalid and cannot be loaded.” (Back-translated from german to english, so original en popup message wwording may be different.)

    Another question not covered in the article: WHEN (how often) is telemetry data gathered and transmitted (and how much is it approximately)? (Interesting while in 3G Data Roaming.)

  7. Thank you Taras and all the team for this beauty and the upcoming releases.

  8. nursoda: you need to install the extension that is named “about:telemetry”. Only then can you view the page called “about:telemetry”.

  9. Oops, sorry, somehow i didnt saw njn’s comment. You can delete mines. :)

  10. About:telemetry extension is not working with FF Nightly 10 so please bump up the support of it, you are missing some realtime data from Nightly users.

  11. Is an effort being made to encourage users to turn this feature on ?

    Would an article explaining the data that can be seen in about:telmetry would help. I doubt there will be any sumo kb written about this (its rather a nightmare to track articles at present)but possibly a link from a sumo article to a blog may be acceptable.

    I also commented on the UI for this in the form of a bug

  12. Since you chose per-session ids, does that mean you can not tell when someone manually restarts FF because it has become too slow for them?