Make Jira open links in a new tab. Code courtesy of Peter Regin https://www.reddit.com/r/jira/comments/8gsv03/greasemonkey_script_to_open_external_links_in_new/dylydyy/

target_blank.js

// ==UserScript==
// @name         Jira Links in new tab
// @description  Target _blank
// @match        https://jira.mesosphere.com/*
// @grant        none
// @version     1.0.1
// ==/UserScript==
function init() {

    $("a")
        .each(function() {
            var href = $(this)
                .attr("href");
            if (href !== undefined && (href.indexOf("http://") >= 0 || href.indexOf("https://") >= 0)) {
                $(this)
                    .attr("target", "_blank");
            }

        });
}


window.addEventListener("load", function() {
    setTimeout(init, 2000);

    $(document)
        .bind("DOMSubtreeModified", function() {
            init();
        });
}, false);