When you set a file in a folder resource as main file, nothing happens. I can't find documentation what it should do, so may be that is my problem
What I expected is that the main file, being an index.html file, would open in the browser and all links in it would work. If you open the folder resource, the main file is the only visible one.
It is off course possible that the option shouldn't be there (it wasn't in the 1.x version)