Start with the simplest task of capturing the URL in Firefox from a C# application. It appears using user32.dll Windows API functions will not work as is the approach for c
One Microsoft tool I ran into:
UI Automation, as part of .NET 3.5 http://msdn.microsoft.com/en-us/library/aa348551.aspx
Here's an example: http://msdn.microsoft.com/en-us/library/ms771286.aspx
I don't have UI Spy on my pc to interrogate Firefox, so I don't know if this will help out with your user32.dll problem.