"For those who, like me, came here looking for instructions on how to disable the new navigation bar, you need to enable secret settings (Settings -> About Firefox -> Tap the firefox logo a bunch of times) and then there will be a toggle under Settin...
The hide functionality has existed in Firefox Mobile since I have first used it, which IIRC I started using it in around 2019-2020. In Settings > Customize you have a toggle called "scroll to hide toolbar" enabling it makes it hide the bar, disabling...
