Shield Study: JavaScript Errors

A Shield study to test collecting JavaScript errors thrown by Firefox chrome code (not errors from webpages themselves).

Overview

This study listens for browser chrome errors being logged to the Browser Console. It then computes a hash based on the error type, name, and stack trace, and sends that hash in a shield-study-addon Telemetry ping along with the user's client ID and environment information.

The purpose of the study is to measure the amount and distribution of browser chrome errors in a privacy-respectful way. The data will be used to create a prototype for collecting these errors to aid in Firefox development.

Dashboards

• Number of study pings received per-minute

Preferences

extensions.shield-study-js-errors@shield.mozilla.org.testing

If true, mark Telemetry pings sent by the client as test pings.

extensions.shield-study-js-errors@shield.mozilla.org.submitIntervalMs

Interval (in milliseconds) at which to submit collected error hashes to telemetry.

extensions.shield-study-js-errors@shield.mozilla.org.expirationDate

Date.parse-compatible string specifying the datetime that the experiment should expire and automatically uninstall itself. Defaults to January 1st, 2018.

extensions.shield-study-js-errors@shield.mozilla.org.expirationIntervalMs

Interval (in milliseconds) at which to check whether the study has expired or not. Defaults to once per day.

Data Collection

The study collects errors by listening to all messages that are being logged to the Browser console and filtering out non-error messages. Then, it filters out errors with categories that the Web console displays, leaving only errors from the Firefox UI itself.

Telemetry Ping Example

Once an hour, if any errors were captured, a Telemetry ping is sent with environmental data and a payload that looks like this:

{
  "version": 3,
  "study_name": "shield-study-js-errors",
  "branch": "default",
  "addon_version": "0.1.0",
  "shield_version": "unset",
  "type": "shield-study-addon",
  "data": {
    "attributes": {
      "fingerprints": "[{\"fingerprint\":\"q35iauGpeCg8FIHj4ptetoBxjIdkuyQi2InIkNpd3AYLwSH7RS44By4CbrPVH0yA\",\"utcTimestampMs\":1512683455924}]",
      "utcTimestampMs": "1512683575918"
    }
  },
  "testing": false
}

The study specific fields are:

data.attributes.fingerprints

A JSON string encoding a list of objects. Each object has a fingerprint, which is a SHA384 hash of the an error type, message, and stacktrace, and a timestamp indicating when the error occurred.

data.attributes.utcTimestampMs

A timestamp indicating when the ping was sent. This is used to deal with inaccurate local time on the client.

Development

To build the add-on, run the make command:

$ make

This will create a shield-study-js-errors.xpi file in the root of the repo containing the add-on.

To test this, you will either need to get the add-on signed by the Mozilla Extension key, or disable the following preferences on a copy of Firefox Nightly:

• xpinstall.signatures.required
• extensions.allow-non-mpc-extensions

Linting can be run on the add-on using make lint:

$ npm install # If they haven't been installed yet
$ make lint

License

Shield Study: JavaScript Errors is licensed under the MPLv2. See the LICENSE file for details.