Handle the link event.

A lot of link in SharePoint 2010 is handle to  “onclick” event,

This is the default link:

<a οnfοcus="OnLink(this)" href="{$thisNode/@FileRef}" οnmοusedοwn="return VerifyHref(this,event,'{$XmlDefinition/List/@DefaultItemOpen}','{$thisNode/@HTML_x0020_File_x0020_Type.File_x0020_Type.mapcon}','{$thisNode/@serverurl.progid}')"

                 οnclick="return DispEx(this,event,'TRUE','FALSE','{$thisNode/@File_x0020_Type.url}','{$thisNode/@File_x0020_Type.progid}','{$XmlDefinition/List/@DefaultItemOpen}','{$thisNode/@HTML_x0020_File_x0020_Type.File_x0020_Type.mapcon}','{$thisNode/@HTML_x0020_File_x0020_Type}','{$thisNode/@serverurl.progid}','{$thisNode/@CheckoutUser.id}','{$Userid}','{$XmlDefinition/List/@ForceCheckout}','{$thisNode/@IsCheckedoutToLocal}','{$thisNode/@PermMask}')">

<a>

You click the a link the “onclick” event will be first handled, when you file is InfoPath form, you want your link open the file by IE,

So you need update the “onclick” event

form  '{$thisNode/@File_x0020_Type.url}'

 to ‘http://[SharePointServer]/Docs/_layouts/FormServer.aspx?XmlLocation=[XmlUrl]  &DefaultItemOpen=1’

&DefaultItemOpen=1 is tell the page open by IE.

my url is:

‘http://sharepoint-test/Docs/_layouts/FormServer.aspx?XmlLocation=/Docs/IHS%20Experse%20Report/July-28th-2010%20by%20leon-11.xml&DefaultItemOpen=1’