I just upgraded from Flash Builder 4.5 to Flash Builder 4.6. Now when I want to run/debug, it does not launch a browser, it will only launch the "adobe flash player 11" window.
I tried setting the browser in "window" / "preferences" / "general" / "web browser" but it makes no difference at all.
Guess what, I just solved this problem.
I had to make it generate the html wrapper, right click on the project, click on properties, "Flex Compiler", tick "Generate HTML wrapper file" (near the bottom of that page). I ticked this, re-compiled and it works.
You see, previously I was using my own html wrapper in Flex builder 4.5 and I had changed it.
You can say this is not ideal, it seems I HAVE to have "Generate HTML wrapper file" ticked for the debugging to work.