With so many browsers on the market, Mozilla is making sure that Firefox 4 stands out from the rest. I saw a demo of what was to be expected from Firefox 4 a couple months back on the web, and I was pretty impressed. As of right now, the Firefox 4 beta is available to download. Here is small sample from a long list of features you can expect from the Firefox 4 Beta directly from the Download Page
New Add-ons Manager and extension management API (UI will be changed before final release)
The Bookmarks Toolbar has been replaced with a Bookmarks Button by default (you can switch it back if you’d like).
Crash protection for Windows, Linux, and Mac when there is a crash in the Adobe Flash, Apple QuickTime or Microsoft Silverlight plugins.
New HTML5 parser.
Web developers can use Websockets for a low complexity, low latency, bidirectional communications API.
- Operating System