I still haven't been able to find a solution to this problem. We have an application that launches a browser window but the underlying third party addin that we are using doesn't support IE9 yet. I know that I can switch to Browser mode for IE8 by tapping F12 and select this.
Is there a way to control this on the startup in the command line? Cause as it is now we have problem when running the application when it opens new windows and automatically tries to execute this third party addin that is required.
And no we haven't an option, we are forced to use this third party addin but would like to support that installation of IE9 as well.
I don't know if you have any control over the content being rendered in the browser, but if you do, IE lets you use META tags to force the browser into a rendering mode of a specific IE version. More info at MSDN right here
Also, further down the page there are instructions on how to set up your web server to tell IE which mode to use when it's requesting the page. (If that is of any use to you)
Unfortunately all information I can find on the subject (and I did a comprehensive search for my own project) indicates that there is no such option, or at least not in the general release of IE.
Here's Microsoft's "official" list of currently supported IE command line options