It sounds like there's an underlying problem with Adobe AIR on your system.
As you are aware, clicking the 'Browse' button should open your system's native file chooser window.
I'm not sure what would prevent the file chooser window from displaying correctly but here are a few things to try:
Suggestion #1
If you have any third-party anti-virus or security software installed, then please try temporarily disabling it in case it is somehow interfering with JuiceboxBuilder-Pro's functionality.
(Please do so at your own risk and be sure to disconnect from the internet first.)
Suggestion #2
Clear all JuiceboxBuilder-Pro preferences and settings.
(1) Close JuiceboxBuilder-Pro
(2) Delete the following folders manually:
(3) Run JuiceboxBuilder-Pro to see if this has resolved the problem.
Suggestion #3
Try uninstalling and then reinstalling Adobe AIR and make sure that you are using the latest version (v33.1.1.444).
You can download it from here: https://airsdk.harman.com/runtime
The problem sounds like an issue with Adobe AIR integrating with your operating system so hopefully a clean AIR installation will help.
Suggestion #4
Make sure that your operating system is up to date and that you have the most recent graphics drivers installed.
I hope that one of these suggestions helps you to resolve your problem.
Please let me know how you get on.
Thank you.