You can still test in Desktop. It'll just have a "trial mode" badge in the upper left. I remember Flash being finicky (on Linux) back when I was using 3.4, but was able to get around any issues. But I was using Build 9180, not 9300.
The reason I asked if desktop worked for you is because if your goal is to create a desktop game, but you're only using Flash for testing purposes, you might as well not waste your time with getting Flash to work and just test on desktop. Scaling issues aside, Flash is more forgiving of some coding mistakes that will suddenly pop up when you go to desktop.