Data Collection

The Snippets Service and the code that it embeds onto about:home collect data about user interaction with snippets in order to help us determine the effectiveness of certain types of snippets and measure whether a specific snippet is successful. This document outlines the types of data we collect and how it is handled.

Retrieving Snippets

The Overview document describes how Firefox retrieves snippets. The actual URL that Firefox uses for fetching snippets can be found under the about:config preference browser.aboutHomeSnippets.updateUrl and defaults to:

The names surrounded by % symbols are special values that Firefox replaces with information about the user’s browser.


A hard-coded number within Firefox specifying which version of about:home is retrieving snippets. We sometimes increase this when about:home changes in a way that may break certain snippets.

Example: 1


The name of the product being used.

Example: Firefox


The Firefox version number currently being used.

Example: 29.0.1


A string uniquely identifying the build of Firefox in use, usually in the form of the date the build occurred with a number appended.

Example: 2007083015


A string describing the platform and configuration used when building Firefox.

Example: Darwin_x86-gcc3


The locale that the current Firefox was built for. We use this for showing snippets in different languages only to users who can read that language.

Example: en-US


The release channel for the current Firefox. This is typically one of release, beta, aurora, or nightly.

Example: aurora


A string describing the operating system that this Firefox was built for.

Example: Darwin%208.10.1


A string used to describe custom distributions of Firefox, such as when providing custom builds with partners. This is set to default for most instances of Firefox.

Example: default


Version of the customized distribution. This is also default for most instances of Firefox.

Example: default


Snippet code, which is executed on about:home, sends HTTP requests to a server located at and/or whenever an event occurs that we would like to measure. These requests are sampled at a rate of 1%, meaning that only 1% of the time an event occurs will a request be made.

Requests sent to contain the following data (sent as URL parameters in the query string) in addition to the normal data available from an HTTP request:

Snippet Name
Unique name referring to the snippet that was being viewed when the request was sent.
The locale of the current Firefox instance (the same locale value described in the snippet URL from the previous section).
The country code corresponding to the country the user is currently located in. This is determined via the user’s IP address and is cached locally within Firefox for 30 days. This value may be empty in cases where we can’t retrieve the user’s country.
A string describing the type of event being measured, such as a snippet impression or a link click.
A string describing the snippet campaign this snippet is related to. We use this to help group metrics across multiple snippets related to a single campaign. This value may be empty.

Types of Metrics Gathered

The following is a list of the types of events that we collect data for as described in the previous section:


An impression is whenever a user is shown a specific snippet.

Snippet Clicks

Whenever a link in a snippet is clicked, we trigger an event that notes which particular link was clicked. This includes links that may trigger an action besides opening up a new page, such as links that trigger browser menus.

Video Plays, Pauses, Replays

Some snippets allow users to view videos. Some of these snippets trigger events when the video is played or paused, when the end of the video is reached, or when the user replays the video after it finishes.

Social Sharing

Some snippets contain popup windows to share content on social networks, such as Facebook or Twitter. Most of these snippets trigger an event when the user launches the popup window.

Default Browser

Some snippets trigger an event that tracks whether Firefox is the default browser on the user’s system. These snippets also trigger an event when the user makes Firefox their default browser by either clicking a link in the snippet or by setting the default outside of the browser.

Browser UI Events

Some snippets trigger events when the user clicks specific buttons in the Firefox user interface (as opposed to the in-page snippet). Examples of the elements that can be tracked this way include:

  • The “Email”, “Copy Link”, and “Start Conversation” buttons within the Firefox Hello dialog.

Google Analytics

The snippets statistics server may proxy data to Google Analytics, with stripped IP information and with a randomly generated UID unique to every request. Google Analytics is never loaded within about:home. Some Mozilla websites use Google Analytics to collect data about user behavior so that we can improve our sites.