Microsoft is trying to stay on par with Mozilla, Google's Chrome and Apple's Safari by introducing more web standards, support for HTML 5, and speeding up the rendering of Javascript for sites that rely heavily on the code base, such as Facebook. Microsoft has not fully embraced the standards community and has found points of contention with the decision of a standard for video codec and HTML 5 support.
According to a couple reports, Internet Explorer held up fairly well in a Javascript-focused speed test.
Microsoft has however seemed to shift it's philosophy towards the web browser. On the IE blog, in an article titled HTML5 and Same Markup: Second IE9 Platform Preview Available for Developers, Microsoft described their push towards standards: “web browsers should render the same markup — the same HTML, same CSS, and same script — the same way… that’s simply not the case today.”
Source: https://blogs.msdn.com/ie/archive/2010/05/05/html5-and-same-markup-second-ie9-platform-preview-available-for-developers.aspx