Android scroll top od DaveRo

On Android, click the 3-dots to get the menu.
Tap 'Add-ons'
Tap 'Scroll to top' to scroll the current tab to the top of the page.

On desktop it adds a green up-arrow icon to the toolbar.

There is a companion add-on - Android scroll bottom

On a responsive site, one which fetches more content automatically when you read to the top it will scroll to the top of what's currently downloaded.