dashboard_drag_scroll.user.js

// ==UserScript==
// @name          Dashboard Drag Scroll
// @namespace     http://d.hatena.ne.jp/arikui/
// @include       http://www.tumblr.com/dashboard
// @include       http://www.tumblr.com/tumblelog/*
// @grunt         none
// ==/UserScript==

var position = {
  mutable: false,
	prev   : null,
	rato   : 14
};

document.addEventListener("mousedown", function(event){
	event.preventDefault();
	event.stopPropagation();

	var targetId = event.target.getAttribute("id");

	if(event.target.tagName != "HTML"){
		if(!targetId || !targetId.match(/^(?:dashboard_index|container|content)$/))
			return;
	}

	position.mutable = true;
	position.prev    = event.clientY;
}, false);

document.addEventListener("mouseup", function(event){
	event.preventDefault();
	event.stopPropagation();

	position.mutable = false;
}, false);

document.addEventListener("mousemove", function(event){
	event.preventDefault();
	event.stopPropagation();

	if(!position.mutable)
		return;

	window.scrollBy(0, - position.rato * (event.clientY - position.prev));
	position.prev = event.clientY;
}, false);