I'm on IE11, Win 8.1. If I set my default browser as IE, when I launch two URLs from an external program, or by running Start "http://microsoft.com" in a PoSh window, I get one window with two tabs.
However, if I manually invoke iexplore like "C:\Program Files\Internet Explorer\iexplore.exe" http://www.microsoft.com/ then I get two separate windows.
I looked in the registry at how the browser is registered, and believed it would be using the command at HKEY_CLASSES_ROOT\IE.HTTP\shell\open\command, however that is set to "C:\Program Files\Internet Explorer\iexplore.exe" %1.
Passing -framemerging appears to have no effect.
So what do I need to do when invoking iexplore.exe to allow it to launch tabs instead of new windows (which is what the Tab settings in IE are set to). I need to be able to do this without IE being the default browser.