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Why does IE9 switch to compatibility mode on my website?

Works in IE9 documentMode for me.

Without a X-UA-Compatible header/meta to set an explicit documentMode, you'll get a mode based on:

  • whether the user has clicked the ‘compatibility view’ button in that domain before;
  • perhaps also whether this has happened automatically due to some other content on the site causing IE8/9's renderer to crash and fall back to the old renderer;
  • whether the user has opted to put all sites in compatibility view by default;
  • whether IE thinks the site is on your intranet and so defaults to compatibility view;
  • whether the site in question is in Microsoft's own list of websites that require compatibility view.

You can change these settings from ‘Tools -> Compatibility view settings’ from the IE menu. Of course that menu is now sneakily hidden, so you won't see it until you press Alt.

As a site author, if you're confident that your site complies to standards (renders well in other browsers, and uses feature-sniffing to decide what browser workarounds to use), I suggest using:

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

or the HTTP header:

X-UA-Compatible: IE=Edge

to get the latest renderer whatever IE version is in use.


I put

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

first thing after

<head>

(I read it somewhere, I can't recall)

I could not believe it did work!!


To force IE to render in IE9 standards mode you should use

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

Some conditions may cause IE9 to jump down into the compatibility modes. By default this can occur on intranet sites.


I've posted this comment on a seperate StackOverflow thread, but thought it was worth repeating here:

For our in-house ASP.Net app, adding the "X-UA-Compatible" tag on the web page, in the web.config or in the code-behind made absolutely no difference.

The only thing that worked for us was to manually turn off this setting in IE8:

enter image description here

(Sigh.)

This problem only seems to happen with IE8 & IE9 on intranet sites. External websites will work fine and use the correct version of IE8/9, but for internal websites, IE9 suddenly decides it's actually IE7, and doesn't have any HTML 5 support.

No, I don't quite understand this logic either.

My reluctant solution has been to test whether the browser has HTML 5 support (by creating a canvas, and testing if it's valid), and displaying this message to the user if it's not valid:

enter image description here

It's not particularly user-friendly, but getting the user to turn off this annoying setting seems to be the only way to let them run in-house HTML 5 web apps properly.

Or get the users to use Chrome. ;-)


The site at http://www.HTML-5.com/index.html does have the X-UA-Compatible meta tag but still goes into Compatibility View as indicated by the "torn page" icon in the address bar. How do you get the menu option to force IE 9 (Final Version 9.0.8112.16421) to render a page in Standards Mode? I tried right clicking that torn page icon as well as the "Alt" key trick to display the additional menu options mentioned by Rene Geuze, but those didn't work.