An anonymous reader writes: Mozilla on Tuesday officially launched Firefox 20 for Windows, Mac, Linux, and Android. The improvements include per-window private browsing, a new download manager in the Firefox toolbar, and the ability to close hanging plugins without the browser hanging. The new desktop version was available as of yesterday on the organization's FTP servers, but that was just the initial release of the installers. Firefox 20 has now officially been made available over on Firefox.com and all users of old Firefox versions should be able to upgrade to it automatically. As always, the Android version is trickling out slowly on the official Google Play Store. The changelogs are here: desktop and Android.