browser.search.separatePrivateDefault is renamed to browser.search.separatePrivateDefault.enabled, and its default is intentionally changed from true to false as part of this rename. This does not change behaviour: the feature remains gated behind browser.search.separatePrivateDefault.featureGate (renamed from .ui.enabled), which defaults to false, so .enabled is only consulted once the feature gate is turned on. Differential Revision: https://phabricator.services.mozilla.com/D321634