ios iphone mobile-safari

Prevent Mobile Safari from presenting toolbar when bottom of viewport is tapped

We have a simple mobile app running in Mobile Safari (MS) on iOS. When the user scrolls down the page n pixels, a “top” button slides up from the bottom. The top button is fixed position. Problem is, when you start scrolling in MS, the navigation and toolbar UI is hidden. When you tap the “top” button, it reveals the bottom toolbar and a second tap is required to tap the “top” button. Is there any way to disable the default “tap on the bottom part of the viewport to reveal the toolbar” behavior so our top button works as expected (i.e. jumps to the top of the page with one click, not two?

No there is not. You can control the content of your webpage but not the behavior of the safari app.