“untrustedModules” ping

This ping contains information about events whereby untrusted modules were loaded into the Firefox process.

  "type": "untrustedModules",
  ... common ping data
  "clientId": <UUID>,
  "environment": { ... },
  "payload": {
    "structVersion": <number>, // See below
    "xulLoadDurationMS": <number>, // Time spent loading xul.dll, in milliseconds (introduced in Firefox 66)
    "errorModules": <number>, // Number of modules that failed to be evaluated
    "events": [ ... ]
    "combinedStacks": { ... },


Version of this payload structure. Reserved for future use; this is currently always 1.


An array, each element representing the load of an untrusted module. Because modules can invoke the load of other modules, there may be multiple modules listed per event.

This array is synchronized with the payload.combinedStacks object which contains the captured stack trace for each event.

A maximum of 50 events are captured.

  "processUptimeMS": <number>, // Number of milliseconds since app startup
  "isStartup": <boolean>, // See below
  "threadID": <unsigned integer>, // Thread ID where the event occurred
  "threadName": <string>, // If available, the name of the thread
  "modules": [
      "moduleName": <string>, // See below
      "loaderName": <string>, // See below
      "loadDurationMS" : <number>, // Optional. Time spent loading this module, in milliseconds (introduced in Firefox 66)
      "baseAddress": <string>, // Base address where the module was loaded, e.g. "0x7ffc01260000"
      "fileVersion": <string>, // The module file version, e.g. ""
      "moduleTrustFlags": <unsigned integer> // See below
    ... Additional modules


  • true if the event represents a module that was already loaded before monitoring was initiated.
  • false if the event was captured during normal execution.


The path to the module file, modified to remove any potentially sensitive information. In most cases, the directory path is removed leaving only the file name, e.g. foo.dll. There are three exceptions:

  • Paths under %ProgramFiles% are preserved, e.g. %ProgramFiles%\FooApplication\foo.dll
  • Paths under %SystemRoot% are preserved, e.g. %SystemRoot%\System32\DriverStore\FileRepository\nvlt.inf_amd64_97992900c592012e\nvinitx.dll
  • Paths under the temporary path are preserved, e.g. %TEMP%\bin\foo.dll


The name of the module as it was requested from the OS. Generally this will be the same as the above moduleName.

This is treated as a path and is modified for privacy in the same way as moduleName above.


This is a bitfield indicating whether various attributes apply to the module.

  • 1 if the module is digitally signed by Mozilla
  • 2 if the module is digitally signed by Microsoft
  • 4 if the module’s version info indicates it’s a Microsoft module
  • 8 if the module is located in the Firefox application directory
  • 0x10 if the module has the same location and version information as the Firefox executable
  • 0x20 if the module is located in the system directory
  • 0x40 if the module is a known keyboard layout DLL
  • 0x80 if the module is an internally-recognized JIT module
  • 0x100 if the module is located in the Windows Side-by-side directory (introduced in Firefox 66)
  • 0x200 if the module is the XPCOM module, xul.dll (introduced in Firefox 66)
  • 0x400 if the module is located in the SysWOW64 directory (introduced in Firefox 66)


This object holds stack traces that correspond to events in payload.events.

"combinedStacks": {
  "memoryMap": [
      <string>, // Name of the module symbol file, e.g. ``xul.pdb``
      <string> // Breakpad identifier of the module, e.g. ``08A541B5942242BDB4AEABD8C87E4CFF2``
    ... Additional modules
  "stacks": [
        <integer>, // The module index or -1 for invalid module indices
        <unsigned integer> // The program counter relative to its module base, or an absolute pc
      ... Additional stack frames (maximum 500)
    ... Additional stack traces (maximum 50)


  • The client id is submitted with this ping.
  • The Telemetry Environment is submitted in this ping.
  • String fields within payload are limited in length to 260 characters.
  • This ping is only enabled on Nightly builds of Firefox Desktop for Windows.
  • This ping is sent once daily.
  • Only events occurring on the main browser process are recorded.
  • If there are no events to report, this ping is not sent.

Version History

  • Firefox 65: Initial support (bug 1435827).

  • Firefox 66:

    • Added Windows Side-by-side directory trust flag (bug 1514694).
    • Added module load times (xulLoadDurationMS, loadDurationMS) and xul.dll trust flag (bug 1518490).
    • Added SysWOW64 trust flag (bug 1518798).