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

Compatibility Mode Woes in IE9: Why and How to Fix

In a perplexing situation, users have noticed that IE9 switches to compatibility mode when accessing a specific website. This issue persists despite removing CSS includes, suggesting that something deeper is causing the browser to revert to its older rendering engine.

Root Cause of Compatibility Mode Switching

IE9 determines its rendering mode based on several factors, including:

• Previous user settings for compatibility view
• Automatic fallback due to script errors
• User preference for default compatibility view
• Intranet site status
• Microsoft's internal list of websites that require compatibility view

Understanding X-UA-Compatible Header and HTTP Header

To override these defaults, website authors can employ the following strategies:

• : Informs IE to use the latest rendering engine, regardless of the version.
• X-UA-Compatible: IE=Edge: HTTP header equivalent of the meta tag.

By implementing these headers, website developers can force IE to render their site using the most up-to-date technology, ensuring a consistent experience across different versions of the browser.

Other Potential Solutions

In addition to the X-UA-Compatible headers, consider the following:

• Manually disabling compatibility mode via the IE menu (Alt Tools)
• Excluding the website from Microsoft's compatibility view list by contacting Microsoft support
• Verifying that your website adheres to web standards and employs feature sniffing to account for browser differences

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