If you're loading it through a C# WinForm control, you might be able to do something like pre-inject a hidden input tag onto the page with a particular name/value, and then in the javascript on the actual page, check for that tag to determine if the page was loaded via a form... I'd guess you'd make a HttpWebRequest out to the resource you want, manipulate the response in some way, then load it into your viewable control... I'm shooting from the hip here, so this is just a guess. I haven't worked in WinForms for a while now.
You might want to look at your approach, however... Are you absolutely in need of having this page be loaded through a WinForm?
Edit: Also the dude suggesting you post this on SO is correct
If you're loading it through a C# WinForm control, you might be able to do something like pre-inject a hidden input tag onto the page with a particular name/value, and then in the javascript on the actual page, check for that tag to determine if the page was loaded via a form... I'd guess you'd make a HttpWebRequest out to the resource you want, manipulate the response in some way, then load it into your viewable control... I'm shooting from the hip here, so this is just a guess. I haven't worked in WinForms for a while now.
You might want to look at your approach, however... Are you absolutely in need of having this page be loaded through a WinForm?
Edit: Also the dude suggesting you post this on SO is correct