User interface

IE9 includes signficant alterations to its user interface when compared with previous versions. These include integration with Windows 7's taskbar providing Pinned Sites, a new security-enabled download manager that manages file transfers and can pause and resume downloads and informs if a file may be malicious, address bar search, enhanced tabs and tab page, and an Add-on Performance Advisor that shows which third party add-ons may be slowing down browser performance and then allows the option to disable or remove them. It introduces a minimalist interface, which brings it more in line with the current interfaces of Chrome and Opera. It is also reminicent of the Windows Live suite.

JScript engine

IE9 features a faster JScript engine than IE8's, internally known as Chakra. Chakra has a separate background thread for compiling JavaScript. Windows runs that thread in parallel on a separate core when one is available. Compiling in the background enables users to keep interacting with webpages while IE9 generates even faster code. By running separately in the background, this process can take advantage of modern multi-core machines. In preliminary SunSpider benchmarks for the third IE9 Platform Preview, it outperformed the IE8 engine by a factor 10 and also outperformed the newest Firefox 4.0 pre-release.

ECMAScript
The Chakra JScript engine significantly improves support for ECMA-262: ECMAScript Language Specification standard, including features new to the recently finalized Fifth Edition of ECMA-262 (often abbreviated ES5).

DOM

DOM improvements include:

• DOM Traversal and Range
• Full DOM L2 and L3 events
• getComputedStyle from DOM Style
• DOMContentLoaded

CSS

CSS improvements include support for portions of the following modules:

• CSS3 Backgrounds and Borders
• CSS3 Values and Units
• CSS3 Media Queries

HTML5

HTML5 Media

IE9 includes support for the HTML5 video and audio tags.
The audio tag will include native support for the MP3 and AAC codecs, while the video tag will natively support H.264/AVC. Support for other video formats, such as WebM, will require third-party plugins.

HTML5 Canvas

IE9 includes support for the HTML5 canvas tag.

HTML5 Inline SVG support

The first IE9 Platform Preview has support for:

• Methods of embedding: inline HTML, inline XHTML,