Open links contained in answers\responses on StackExchange, StackOverflow, AskUbuntu, and SuperUser in a new tab. Marks all edited links with a unicode checkbox followed by the link in red for visibility.

superStackOverEx.js

// ==UserScript==
// @name           Add _blank to StackExchange\StackOverflow\Others
// @description    Open StackExchange\StackOverflow\Other links in a new tab
// @namespace      https://rawgit.com/rabel001/userscripts/master/superStackOverEx.js
// @updateURL      https://rawgit.com/rabel001/userscripts/master/superStackOverEx.js
// @downloadURL    https://rawgit.com/rabel001/userscripts/master/superStackOverEx.js
// @version        1.00
// @author         rabel001
// @include        *superuser.com*
// @include        *askubuntu.com*
// @include        *stackoverflow.com*
// @include        *stackexchange.com*
// @grant          none
// ==/UserScript==

(() => {
	'use strict';

	var pages = [
		"askubuntu.com",
		"superuser.com",
		"stackoverflow.com",
		"stackexchange.com"
	];

	var contains = (iArray, iNeedle) => {
		for(var i in iArray) {
			if(iArray[i] == iNeedle) {
				return true;
			}
		}
		return false;
	}

	var setBlank = (elem, page) => {
		//function setBlank(elem) {
		elem.setAttribute('target', '_blank');
		switch(page) {
			case pages.stackoverflow:
				try {
					elem.style.fontSize = '15px';
					elem.style.color = 'red';
					var code = elem.getElementsByTagName('code').item(0);
					var nStyle = 'font-size: 15px; font-family: Arial,"Helvetica Neue",Helvetica,sans-serif; line-height: 1.26666667;';
					var newstyle = (code.getAttribute('style') == null) ? nStyle : code.getAttribute('style') + '' + nStyle;
					code.setAttribute('style', newstyle);
				} catch(e) {}
				break;
		}
	};

	var ErrorArray = [];
	var setBallotbox = (elem, page) => {
		var span = document.createElement('span');
		span.innerHTML = "☑ "; //"☑ "; //"✔ "; //"▣ ";
		span.id = "ascii-ballotbox";
		span.style.color = "red";
		span.style.fontSize = 'large';
		try {
			elem.insertAdjacentElement('beforebegin', span);
		} catch(err) {
			elem[0].insertAdjacentElement('beforebegin', span);
			ErrorArray.push(elem);
		}
	};

	var recursiveElements = (elem, page) => {
		if(elem.tagName == "A") {
			setBlank(elem, page);
			setBallotbox(elem, page);
		} else {
			var innerArr = [].slice.call(elem.children);
			innerArr.forEach(function(child) {
				recursiveElements(child, page);
			});
		}
	};

	var setBlanks = () => {
		var posttext = document.querySelectorAll('.post-text');
		posttext.forEach(function(elem) {
			var ahrefs = elem.getElementsByTagName('a');
			var count = ahrefs.length;
			switch(true) {
				case(count === 1):
					setBlank(ahrefs.item(0), pages.stackoverflow);
					setBallotbox(ahrefs, pages.stackoverflow);
					break;
				case(count > 1):
					Array.prototype.slice.call(ahrefs).forEach(function(elem2) {
						recursiveElements(elem2, pages.stackoverflow);
					});
					break;
				default:
					break;
			}
		});
	};

	var splitHostName = location.hostname.split('.');
	var host = splitHostName[splitHostName.length - 2];
	var root = splitHostName[splitHostName.length - 1];
	var hostname = `${host}.${root}`;
	if(contains(pages, hostname)) {
		setBlanks();
	}
})();