When archiving is enabled through the relevant pref (toolkit.telemetry.archive.enabled), pings submitted to TelemetryController are also stored locally in the user profile directory, in <profile-dir>/datareporting/archived.

To allow for cheaper lookup of archived pings, storage follows a specific naming scheme for both the directory and the ping file name: <YYYY-MM>/<timestamp>.<UUID>.<type>.jsonlz4.

  • <YYYY-MM> - The subdirectory name, generated from the ping creation date.

  • <timestamp> - Timestamp of the ping creation date.

  • <UUID> - The ping identifier.

  • <type> - The ping type.

Archived data can be viewed on about:telemetry.


Archived pings are not kept around forever. After startup of Firefox and initialization of Telemetry, the archive is cleaned up if necessary.

  • Old ping data is removed by month if it is older than 60 days.

  • If the total size of the archive exceeds the quota of 120 MB, pings are removed to reduce the size of the archive again.