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IE 9's improvements include the new feature set, the new hardware-accelerated, standards-based rendering, and more.
The RC version adds a Tracking Protection feature in response to the US Federal Trade Commission (FTC) proposal called "Do Not Track" (which I discussed last month in “What You Need to Know About Windows 8, IE 9 Anti-Tracking, Small Business Server, and Microsoft Office Security,” InstantDoc ID 129298). But it also adds some other new features.
First up is the very latest rendering engine, which is derived from the IE 9 Platform Preview releases Microsoft shipped between the September beta release and the end of 2010. This engine has been dramatically improved, and users will notice the performance difference. (Microsoft reports that the new rendering engine is over 350 percent faster than the version included in the beta.)
Next up is a refined UI. This includes nicely squared off and modern-looking UI elements such as the tabs, new address bar treatments, and other niceties.
The RC will also include a new ActiveX Filtering feature that will let users—and admins, via Group Policy—to control which ActiveX controls can display. This will be integrated with the Tracking Protection feature from a UI perspective. As before, I expect the final release of IE 9 to occur before or during the MIX11 conference, which starts April 12, 2011.
source:supersite