1-You can try deleting the "Macromedia" folder in the ~/Library/Preferences/ folder. Others have reported success with this.
2-If you are using the FlashFireBug plugin for Firefox, uninstall it. Other's have reported incompatibility problems with it.
Thanks for the suggestions, but neither made a difference.
It still opens fullscreen then snaps back to the frame, but the frame moves to top left, minus about 50px, so it's under the menu bar and off to the left.
It's as if it's got some weird reference for the size of the frame and where it is, but it doesn't appear to be getting it from any of the FWCS5 preferences, I went right through the system uninstalling everything Adobe/Macromedia from every library/system folder, even managing to reset the trial counter (until it logged into my Adobe ID) but it still does it when installed.
I wish I could find the conflicting app - it's a real PITA.
After a couple of hours fruitless application conflict searching I stumbled on a solution.
I tried the FW without the frame, and didn't like the way the bottom bar sat by the dock, so I turned on dock hiding, the bottom bar then snaps to the bottom of the screen.
Went back to application frame on and was amazed to find that everything was now working as expected.
I assumed it was to do with dock hiding, so unhid it, but FW still works fine. Thought maybe it was to do with the number of icons in the dock (I have over 40) or the dock size, but can't replicate the problem in my other user account, so I can only assume the following:
During the course of an editing session with multiple windows open and maybe with the FW window pushed under the dock and maybe opening a new file from finder in FW - maybe this is when it gets confused. - that would be a typical work pattern for me.
So, no matter any more, I have a fix for next time - hide the dock, see if it resolves, if not hide the dock allow it to open in the non frame mode to full edges of the screen, see if that fixes it.
It explains why a pristine user doesn't have the problem - small dock, it explains why a fresh install is okay for a while - dock not full of applications *I Must Have* maybe someone somewhere can replicate the bug and fix it.
Thanks! I was having a similar problem in Photoshop CS5 in OSX Lion where the document window wouldn't show and I had to switch to application frame to see the document. I moved the dock and the window popped right up!
What a weird glitch.