I'm working in FlashDevelop. I was able to set it up so that I can debug the application by specifying URL in Test Project setting "Open Document". It works, I'm able to press Play in FlashDevelop, it launches my application in a browser and I'm able to set break points, etc.
This feature stops working when I save the FLA project as XFL. When I press play, the application builds successfully but it does not launch in a browser. I get no errors or warnings in output.
update
Here is my set up. I have Flash Developer and Flash Professional open. When I press Play "debug" in Flash Developer, it kicks off a build in Flash Professional project.
Here is what's different if I try to open .FLA project vs when I have it open in .XFL:
If I open a project as .FLA (in Flash Pro), when the build completes, Flash Developer knows about it and executes a post build step of opening a document and attaching a debug session to it.
When I open the project as .XFL (in Flash Pro), when the build completes, Flash Developer doesn't do anything.
My guess there needs to be some communication coming from Flash Professional to Flash Develp saying "hey I'm done building, do whatever post build steps you have set up".