How to navigate to top/bottom of page in mobile firefox

You should add an add-on to help accomplish what you asked. Top and Bottom scroll buttons adds buttons to scroll to the top or bottom of a page.

This extension adds two beautiful buttons at the corner of each page for fast scrolling to the top or the bottom of the page.

The buttons are customisable. You can change its size, transparency, position and the way they are scrolling.
You can also set the buttons to auto hide so you'll see them only when you want.

Disclaimer: I am just a user of the addon, not related to its developer.