Summary

Intent

The changes fix the IAB Ads DevTools toggle behavior in the Firefox New Tab page's Discovery Stream admin panel. The bug relates to the billboard and leaderboard ad size options, which should be mutually exclusive (only one can be active at a time), but the previous implementation using separate toggle switches allowed both to be enabled simultaneously. Additionally, toggling these options did not trigger a cache refresh, meaning changes wouldn't take effect immediately.

Solution

The solution replaces the two separate switches for billboard and leaderboard banner sizes with a single dropdown control that has three options: "Off", "Billboard", and "Leaderboard". This inherently enforces mutual exclusivity between the two banner sizes at the UI level.

Key implementation details:

1. New dropdown: The billboard and leaderboard toggles are replaced with a element containing three elements. Since emits native DOM change events (not React synthetic events), a ref-based approach is used to attach/detach the event listener directly on the DOM node.

2. Ref management: A new method handles attaching and cleaning up the native event listener on the element, including proper cleanup in .

3. Centralized placement update logic: A new method consolidates the logic for updating all IAB-related preferences. It accepts a map of placement states, conditionally dispatches pref changes only when values differ from current state, updates the spoc placements/counts arrays, manages contextual banner prefs, and crucially calls at the end to ensure changes take effect immediately.

4. Refactored : The existing toggle handler (still used for the medium rectangle toggle) now builds a object and enforces mutual exclusivity between billboard and leaderboard before delegating to .

5. CSS additions: New styles are added for the class to properly layout the dropdown, along with various styling improvements for the personalization/inferred overrides sections of the admin panel.

6. Tests: New test cases verify that billboard and leaderboard are kept mutually exclusive, that the change handler works correctly with proper event listener setup/teardown, and that cache refresh is triggered after toggling the medium rectangle.

There are PREFS used in here and with the new PrefsConstants file, I will update the prefs usage once that lands.

r+! nice work

So it turns out the Leaderboard ad size is no longer supported, and per Amber's comment in Bug 2030401 we want to remove all code related to it. Was the intention of this patch to prevent the billboard and leaderboard from being enabled simultaneously? If so, we can just keep the old billboard toggle, and remove the leaderboard toggle.

This revision makes changes to files both inside and in files outside of it. The New Tab page for Firefox Desktop supports train-hopping — a mechanism that allows New Tab code to be deployed to Beta and Release channels independently of the standard release train. Cross-layer changes can break train-hop compatibility, which may block New Tab deployments until fixes reach Release through normal channels.

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