Running some application as a child process is generally a very bad thing. Processes are well isolated from each other; so you won't have sufficient control over the child process; your parent process and child process won't behave like integrated in one application.
Also, you cannot know for sure what Web browser is used by your user.
So, consider much better alternative: host a WebBrowser control in your MFC application. It comes without any additional controls like address bar or anything like that.
Start here:
http://msdn.microsoft.com/en-us/library/ie/aa752046%28v=vs.85%29.aspx[
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—SA