Unlike IE9, the newest upcoming Firefox 4 browser is still supporting Windows XP and even Windows 2000. Currently, you can download Firefox 4 RC (Release Candidate) version to try out and give them feedback on new Firefox 4. Firefox 4 RC is currently available on Mac, Windows and Linux. If your OS is still running on Windows XP or Windows 2000, you can still using latest Firefox 4 browser to enjoy the latest browser technologies.
Firefox 4 team is working hard to produce the better Firefox browser by adding some awesome new features such as improvement on speed in start-up time and page load performance. You can expect the new Firefox 4 is focusing on user’s web experience. Mozilla Firefox 4 also helps users to stop websites from monitoring what they browse on the web. This feature is called “Do Not Track” that helps you to prevent other websites from tracking your browsing behavior. There are more great Firefox 4 features where you can find out on Firefox 4 RC Features page.
Others New Enhancements in Firefox 4
1) Added Vietnamese localization language into Firefox 4
2) Blacklisted a few invalid HTTPS certificates
3) Support the HTML5
4) Support for HSTS security protocol allowing sites to insist that they only be loaded over SSl.
5) Gives user a visual overview of all open tabs, allowing them to be sorted and grouped
More new improved FireFox 4 features can be read from Firefox 4 RC Release Notes