Why Does IE9 Switch to Compatibility Mode and How Can I Prevent It?

IE9 Compatibility Mode and HTML5 Websites

Users encounter IE9 switching to compatibility mode on certain websites, rendering HTML5 content in a diminished fashion. This article investigates the underlying cause and provides a solution to maintain automatic compatibility mode.

Compatibility Mode Factors

In the absence of an X-UA-Compatible header, IE9 selects a compatibility mode based on several factors:

• User-configured settings
• Crashes caused by rendering issues
• Default preferences for intranet sites
• Microsoft's internal compatibility view list

Resolution

To ensure the desired compatibility mode, site authors can explicitly set it using the X-UA-Compatible meta tag or HTTP header. By specifying "IE=Edge," websites can force the use of the latest IE renderer, regardless of version.

Sample Code

<meta http-equiv="X-UA-Compatible" content="IE=Edge">

X-UA-Compatible: IE=Edge

By implementing this solution, websites can override any automatic compatibility mode settings, guaranteeing accurate rendering of HTML5 content in IE9 and subsequent versions.

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