继昨日Firefox 20.0b3正式版发布之后，Mozilla今天又发布了Firefox 20.0 beta4版本，支持了全新的下载窗口。
以下是更新列表和下载地址：
What’s New
NEW
Per-window Private Browsing
Known Issues
NEW
New download experience
NEW
Ability to close hanging plugins, without the browser hanging
NEW
Firefox will offer to reset the Awesomebar
search provider, if it has been changed by third-party software or
through about:config
CHANGED
Continued performance improvements around common browser tasks (page loads, downloads, shutdown, etc.)
DEVELOPER
Continued implementation of draft ECMAScript 6 - clear() and Math.imul
DEVELOPER
New JavaScript Profiler tool
HTML5
<canvas> now supports blend modes
HTML5
Various <audio> and <video> improvements
HTML5
getUserMedia implemented for web access to the user's camera and microphone (with user permission)
FIXED
Details button on Crash Reporter
(793972)
FIXED
Unity plugin doesn't display in HiDPI mode
(829284)
Unresolved
If you try to start Firefox using a locked profile, it will crash (see 573369)
Unresolved
Mootools 1.2.x incompatible with Firefox 18 and newer.Fixed in Mootools 1.3 and newer (see 789036)
Unresolved
Some function keys may not work when pressed (see 833719)
Unresolved on v19
Resolved in v21
官方CDN下载：
20.0b4
http://download.cdn.mozilla.net/pub/mozilla.org/firefox/releases/20.0b4/win32/zh-CN/
19.0.2
http://download.cdn.mozilla.net/pub/mozilla.org/firefox/releases/19.0.2/win32/zh-CN/