how can i jump to the top of a page or a site (facebook as example)
Refresh your page and automatically you ll be in top of the page
Firefox for Android does not have a way to scroll large distances at this time. We are working on either adding fast scrolling as a gesture or using a touchable scrollbar.
On a PC, you can jump to the top of the page by hitting the Ctrl & Home keys simultaneously. You can jump to the bottom of the page by hitting Ctrl & End simultaneously.