Browser Usage Telemetry

The BrowserUsageTelemetry.sys.mjs module is the main module for measurements regarding the browser usage (e.g. tab and window counts, search counts, …).

The measurements recording begins right after the SessionStore has finished restoring the session (i.e. restoring tabs/windows after Firefox starts).

Tab and window interactions

The usage telemetry module currently measures these interactions with the browser’s tabs and windows:

  • tab and window engagement: counts the number of non-private tabs and windows opened in a subsession, after the session is restored (see e.g. browser.engagement.max_concurrent_tab_count);

  • URI loads: counts the number of page loads (doesn’t track and send the addresses, just the counts) directly triggered by the users (see browser.engagement.total_uri_count);

  • navigation events: at this time, this only counts the number of time a page load is triggered by a particular UI interaction (e.g. by searching through the URL bar, see browser.engagement.navigation.urlbar).

Please see Scalars.yaml for the full list of tracked interactions.

Customizable UI

This telemetry records information about the positions of toolbar items and when the user interacts with them. It is submitted as scalar values along with the normal telemetry ping. There are a number of different parts to this telemetry:

UI Areas

For the purposes of this telemetry a set of areas are defined:

  • In the main browser UI:

    • menu-bar - The main menu.

    • menu-toolbar - The normally hidden toolbar that holds the main menu.

    • titlebar - The optional title bar.

    • tabs-bar - The area where tabs are displayed.

    • bookmarks-bar - The bookmarks toolbar.

    • app-menu - The main application (hamburger) menu.

    • tabs-context - The context menu shown from right-clicking a tab.

    • content-context - The context menu shown from right-clicking the web page.

    • widget-overflow-list - Items that have overflowed the available space.

    • pinned-overflow-menu - Items that the user has pinned to the toolbar overflow menu.

    • pageaction-urlbar - Page actions buttons in the address bar.

    • pageaction-panel - The page action (meatball) menu.

    • nav-bar-start - The area of the navigation toolbar before the address bar.

    • nav-bar-end - The area of the navigastion toolbar after the address bar.

    • unified-extensions-area - The unified extensions panel.

  • In about:preferences the different cagtegories are used:

    • preferences-paneGeneral

    • preferences-paneHome

    • preferences-panePrivacy

    • preferences-paneSearch

    • preferences-paneSearchResults

    • preferences-paneSync

    • preferences-paneContainers

Widget Identifiers

In order to uniquely identify a visual element a set of heuristics are used:

  1. If the element is one of the customizable toolbar items then that item’s ID is used.

  2. If the DOM element has an ID set then that is used.

  3. If the DOM element’s class contains one of bookmark-item, tab-icon-sound or tab-close-button then that is used.

  4. If the DOM element has a preference key, command, observes or data-l10n-id attribute then that is used.

  5. If there is still no identifier then this is repeated for the DOM element’s parent element.

Widget Locations

The keyed scalar browser.ui.toolbar_widgets records the position of widgets in the UI. At startup the positions of widgets are collected and recorded by setting the scalar key <widget id>_pinned_<area> to true. The widget ID are the IDs of the elements in the DOM. The area is one of the areas listed above from the browser UI that can be customised.

For the areas that can be controlled the scalar keys <area>_<off/on/newtab> are set. newtab is special to the Bookmarks Toolbar and is used when the toolbar will only be shown on the New Tab page.

Widget Customization

The scalar browser.ui.customized_widgets records whenever the user moves a widget around the toolbars or shows or hides some of the areas. When a change occurs the scalar with the key <widget id>_<action>_<old area>_<new area>_<reason> is incremented. The action can be one of move, add or remove. Old area and new area are the previous and now locations of the widget. In the case of add or remove actions one of the areas will be na. For areas that can be shown or hidden the areas will be off or on. The reason is a simple string that indicates what caused the move to happen (drag, context menu, etc.).

UI Interactions

The scalars browser.ui.interaction.<area> record how often the use interacts with the browser. The area is one of those above with the addition of keyboard for keyboard shortcuts.

When an interaction occurs the widget’s identifier is used as the key and the scalar is incremented. If the widget is provided by an add-on then the add-on identifier is dropped and an identifier of the form addonX is used where X is a number. The number used is stable for a single session. Every time the user moves or interacts with an add-on the same number is used but then the numbers for each add-on may change after Firefox has been restarted.

Profile Count

The scalar browser.engagement.profile_count records how many profiles have been used by the current Firefox installation. It reports a bucketed result, which will be 0 if there is an error. The raw value will be reported for 1-10, but above that, it will report 10 for 10-99, 100 for 100-999, 1000 for 1000-9999, and 10000 for any values greater than that.

The profile count data for an installation is stored in the root of the update directory in a file called profile_count_<install hash>.json. The full path to the file will typically look something like C:\ProgramData\Mozilla\profile_count_5A9E6E2F272F7AA0.json.

This value is meant to be resilient to re-installation, so that file will not be removed when Firefox is uninstalled.

Context menu entrypoints

Some context menus are re-used in multiple places. By default, we simply count the number of interactions per item within a context menu, and do not record the entrypoint that caused the context menu to open.

It is possible to opt-in to recording the entrypoint that caused the context menu to open. This is done by adding an entry to ENTRYPOINT_TRACKED_CONTEXT_MENU_IDS, mapping the ID of the context menu to a keyed Scalar under browser.ui.interaction.. This scalar is recorded only if an interaction is recorded within the context menu itself.

When the keyed scalar is recorded, the key will be a unique ID for the trigger node that caused the context menu to open. The value is the count of openings from that trigger node.