Tried installing the beta in a non-default folder. Selected "Custom" under location to install into, then selected a subfolder under the Applications folder. Only the app file installed in that folder, nothing else. When I tried to run it FF generated an exception message as it couldn't find the necessary .xml file.
I then installed it using the default location in the Applications folder and everything installed correctly and the app started up correctly. I then moved the entire FF4 app folder into the other subfolder and it opens correctly know.
Bug report also filed with the exception message.
Jim in Atlanta, GA