middleMousePaste.uc.js

// ==UserScript==
// @name           middleMousePaste
// @namespace      http://d.hatena.ne.jp/Cherenkov/
// @description    enable overwrite.
// @include        chrome://browser/content/browser.xul
// ==/UserScript==

(function(){
if (gPrefService.getBoolPref("middlemouse.paste")) return alert("Please set a value.\nabout:config -> middlemouse.paste -> false");
window.addEventListener("click", function(event) {
	if (event.button == 1) {
		var target = event.target;
		var tagName = target.tagName;
		if (tagName) tagName = tagName.toLowerCase();
		var type = target.type;
		if (type) type = type.toLowerCase();
		if ((tagName == "input" && (type == "" || type == "text" || type == "password")) || tagName == "textarea" || tagName == "textbox" || tagName == "searchbar") {
			var front = target.value.substr(0,target.selectionStart);
			var back = target.value.substr(target.selectionEnd);
			var select = target.value.substring(target.selectionStart, target.selectionEnd);
			var clipbrd = readFromClipboard();
			if(!clipbrd) clipbrd = "";
			target.value = front + clipbrd + back;
			//modify caret position.
			target.selectionStart = target.selectionEnd = (front.length + clipbrd.length);
		}
	}
}, true);

//stop a scroll event.
window.addEventListener("mousedown", function(event) {
	if (event.button == 1) {
		var target = event.target;
		var tagName = target.tagName;
		if (tagName) tagName = tagName.toLowerCase();
		var type = target.type;
		if (type) type = type.toLowerCase();
		if ((tagName == "input" && (type == "" || type == "text" || type == "password")) || tagName == "textarea" || tagName == "textbox") {
			event.stopPropagation();
		}
	}
}, true);
})();