feedly.user.js

// ==UserScript==
// @name           Feedly Tweak - Open feed item in background by pressing 'i'
// @namespace      http://micbase.com/feedly-tweak-open-item-background-tab-firefox
// @description    Feedly Tweak - Open feed item in background by pressing 'i'
// @include        http*://feedly.com/*
// @grant          GM_openInTab
// ==/UserScript==

var x;
var link;

document.addEventListener('keypress', function(event) {
    //if user press 'i' key, then open links in new tab in background
    if (event.which == 105) {

        x = document.getElementsByClassName('selectedEntry');
        //if no feed item selected, exit
        if (x == null){
            return;
        }
        link = x[0].getAttribute('data-alternate-link');
        event.stopPropagation();
        event.preventDefault();
        GM_openInTab(link, true);
    }
}, true);