Twitter: Rectangular avatars

twitter-rect-avatars.user.js

// ==UserScript==
// @name     Twitter: Rectangular avatars
// @include  http://twitter.com/*
// @include  https://twitter.com/*
// @include  http://tweetdeck.twitter.com/*
// @include  https://tweetdeck.twitter.com/*
// ==/UserScript==

function addGlobalStyle(css) {
    var head, style;
    head = document.getElementsByTagName('head')[0];
    if (!head) { return; }
    style = document.createElement('style');
    style.type = 'text/css';
    style.innerHTML = css;
    head.appendChild(style);
}

addGlobalStyle('.avatar { border-radius: 0 !important; }');