“core” ping

This mobile-specific ping is intended to provide the most critical data in a concise format, allowing for frequent uploads.

Since this ping is used to measure retention, it should be sent each time the browser is opened.

Submission will be per the Edge server specification:

  • docId is a UUID for deduping
  • docType is “core”
  • appName is “Fennec”
  • appVersion is the version of the application (e.g. “46.0a1”)
  • appUpdateChannel is “release”, “beta”, etc.
  • appBuildID is the build number

Note: Counts below (e.g. search & usage times) are “since the last ping”, not total for the whole application lifetime.


  "v": 10, // ping format version
  "clientId": <string>, // client id, e.g.
                        // "c641eacf-c30c-4171-b403-f077724e848a"
  "seq": <positive integer>, // running ping counter, e.g. 3
  "locale": <string>, // application locale, e.g. "en-US"
  "os": <string>, // OS name.
  "osversion": <string>, // OS version.
  "device": <string>, // Build.MANUFACTURER + " - " + Build.MODEL
                      // where manufacturer is truncated to 12 characters
                      // & model is truncated to 19 characters
  "arch": <string>, // e.g. "arm", "x86"
  "profileDate": <pos integer>, // Profile creation date in days since
                                // UNIX epoch.
  "defaultSearch": <string>, // Identifier of the default search engine,
                             // e.g. "yahoo".
  "displayVersion": <string>, // Version displayed to user, e.g. 57.0b3 (optional)
  "distributionId": <string>, // Distribution identifier (optional)
  "campaignId": <string>, // Adjust's campaign identifier (optional)
  "created": <string>, // date the ping was created
                       // in local time, "yyyy-mm-dd"
  "tz": <integer>, // timezone offset (in minutes) of the
                   // device when the ping was created
  "sessions": <integer>, // number of sessions since last upload
  "durations": <integer>, // combined duration, in seconds, of all
                                // sessions since last upload
  "searches": <object>, // Optional, object of search use counts in the
                        // format: { "engine.source": <pos integer> }
                        // e.g.: { "yahoo.suggestion": 3, "other.listitem": 1 }
  "experiments": [<string>, /* … */], // Optional, array of identifiers
                                // for the active experiments
  "accessibilityServices": [<string>, /* … */], // Optional, array of identifiers for
                                                // enabled accessibility services that
                                                // interact with our android products.
  "flashUsage": <integer>, // number of times flash plugin is played since last upload
  "defaultBrowser": <boolean> // true if the user has set Firefox as default browser
  "bug_1501329_affected": <boolean>  // true if Firefox previously used canary clientId
                                     // when submitting telemetry


Field details


The device field is filled in with information specified by the hardware manufacturer. As such, it could be excessively long and use excessive amounts of limited user data. To avoid this, we limit the length of the field. We’re more likely have collisions for models within a manufacturer (e.g. “Galaxy S5” vs. “Galaxy Note”) than we are for shortened manufacturer names so we provide more characters for the model than the manufacturer.


The distributionId contains the distribution ID as specified by preferences.json for a given distribution. More information on distributions can be found here.

It is optional.


The campaignId contains the campaign identifier like ‘3ly8t0’. It’s generated by Adjust, It can only used to identify a campaign, but can’t target to a specific user.

It is optional because not everyone has a campaign to begin with.


On Android, this field may be null. To get the engine, we rely on SearchEngineManager#getDefaultEngine, which searches in several places in order to find the search engine identifier:

  • Shared Preferences
  • The distribution (if it exists)
  • The localized default engine

If the identifier could not be retrieved, this field is null. If the identifier is retrieved, we attempt to create an instance of the search engine from the search plugins (in order):

  • In the distribution
  • From the localized plugins shipped with the browser
  • The third-party plugins that are installed in the profile directory

If the plugins fail to create a search engine instance, this field is also null.

This field can also be null when a custom search engine is set as the default.

sessions & durations

On Android, a session is the time when Firefox is focused in the foreground. sessions tracks the number of sessions since the last upload and durations is the accumulated duration in seconds of all of these sessions. Note that showing a dialog (including a Firefox dialog) will take Firefox out of focus & end the current session.

An implementation that records a session when Firefox is completely hidden is preferable (e.g. to avoid the dialog issue above), however, it’s more complex to implement and so we chose not to, at least for the initial implementation.


On Android, this value is created at profile creation time and retrieved or, for legacy profiles, taken from the package install time (note: this is not the same exact metric as profile creation time but we compromised in favor of ease of implementation).

Additionally on Android, this field may be null in the unlikely event that all of the following events occur:

  1. The times.json file does not exist
  2. The package install date could not be persisted to disk

The reason we don’t just return the package install time even if the date could not be persisted to disk is to ensure the value doesn’t change once we start sending it: we only want to send consistent values.


This describes the search engine usage(count). The format is { “<engine identifier>.<source>”” : count } This is optional because the users may have never used the search feature. There’s no difference if extended telemetry is enabled (prerelease builds) or not.

Possible value :


<engine identifier>: the identifier of the the search engine. The identifier is collected the way same as desktop. we only record the search engine name when:

  • builtin or suggested search engines with an ID (includes partner search engines in various distribution scenarios). If it’s not a built-in engine, we show “null” or “other”.
  • If the user has “Health Report” and core ping enabled.

<sources>: it’s from one of the ‘method’s in UI telemetry. Possible values:

  • actionbar: the user types in the url bar and hits enter to use the default search engine
  • listitem: the user selects a search engine from the list of secondary search engines at the bottom of the screen
  • suggestion: the user clicks on a search suggestion or, in the case that suggestions are disabled, the row corresponding with the main engine


This describes which accessibility services are currently enabled on user’s device and could be interacting with our products. This is optional because users often do not have any accessibility services enabled. If present, the value is a list of accessibility service ids.

Other parameters

HTTP “Date” header

This header is used to track the submission date of the core ping in the format specified by rfc 2616 sec 14.18, et al (e.g. “Tue, 01 Feb 2011 14:00:00 GMT”).

Version history

  • v9:
    • Apr 2017: changed arch to contain device arch rather than the one we built against & accessibilityServices
    • Dec 2017: added defaultBrowser to know if the user has set Firefox as default browser (Dec 2017)
    • May 2018: added (optional) displayVersion to distinguish Firefox beta versions easily
  • v8: added flashUsage
  • v7: added sessionCount & sessionDuration & campaignId
  • v6: added searches
  • v5: added created & tz
  • v4: profileDate will return package install time when times.json is not available
  • v3: added defaultSearch
  • v2: added distributionId
  • v1: initial version - shipped in Fennec 45.


  • distributionId (v2) actually landed after profileDate (v4) but was uplifted to 46, whereas profileDate landed on 47. The version numbers in code were updated to be increasing (bug 1264492) and the version history docs rearranged accordingly.

Android implementation notes

On Android, the uploader has a high probability of delivering the complete data for a given client but not a 100% probability. This was a conscious decision to keep the code simple. The cases where we can lose data:

  • Resetting the field measurements (including incrementing the sequence number) and storing a ping for upload are not atomic. Android can kill our process for memory pressure in between these distinct operations so we can just lose a ping’s worth of data. That sequence number will be missing on the server.
  • If we exceed some number of pings on disk that have not yet been uploaded, we remove old pings to save storage space. For those pings, we will lose their data and their sequence numbers will be missing on the server.

Note: we never expect to drop data without also dropping a sequence number so we are able to determine when data loss occurs.