Is it possible to make so that Firefox can scroll the bottom of the page all the way to the top? Does any browser have this feature?
Geany, which is an IDE, can do this. I sometimes find it useful when having another window open in front and I can still scroll to see everything in the whole document without defocus or move the other window.
If you just want to scroll to the top instantly, the <home> button on your keyboard is what you're looking for.
Other than that, there are several autoscrolling addons for firefox. Just go get one of those.
You can assign a gesture to do it in OS X. I have mine set so that a vertical 3-finger swipe takes me to the top or bottom of a page.
CMD+up or CMD+dn will also do it.
In firefox pressing the HOME key (or Control+HOME) will scroll to the top of the page.
Pressing the END key (or Control+END) will scroll to the bottom of the page
If you want to insert links that do that you can use anchor names and put a <a id="top" name="top"></a> at the top of the document, and a <a id="bottom" name="bottom"></a> at the bottom of the document and use the links <a href="#bottom">Scroll to bottom</a>