Yep, it's been fixed by 1740289. When the root content becomes non-scrollable, now Gecko notifies it so if GeckoView apps can handle the notification properly, the toolbar gets visible.
Bug 1665973 Comment 4 Edit History
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Yep, it's been fixed by bug 1740289. When the root content becomes non-scrollable, now Gecko notifies it so if GeckoView apps can handle the notification properly, the toolbar gets visible.