Some features have a checkbox on the Settings page, such as the new sidebar design with a persistent vertical button bar: General panel, Browser Layout section, "Show sidebar" Other features have a hidden on/off switch on the about:config page ([[Configuration Editor for Firefox]]), such as: * Tab groups browser.tabs.groups.enabled [now true by default in Fx139] * Search engine selector in address bar: browser.urlbar.scotchBonnet.enableOverride [ still ''false'' by default in Fx139] When Mozilla mentions that a new feature is being progressively enabled or gradually rolled out, it usually indicates that a "study" is being used to switch the feature from off to on. If you disabled studies, that could explain why these features are not getting turned on for you during the initial roll-out. To check on that: * [[About Studies]] * [[Manage Firefox data collection and privacy settings]]