Very good news about the offline version of GlowScript: you can now save your program or a compiled html version directly to your Download folder. See the details in README file in the latest version, which you can download at
Basically, you simply click the new Save button to save your program, or click the Export button followed by clicking the Save button to export an html file, ready for execution or embedding in your own web page.
A browser cannot write to an arbitrary location on your hard drive, but I had failed to learn that there is a way for the browser to write to your Download folder.
Bruce