@microbit-josephine could you test this in macOS Safari 6, 9 and 10, and Windows IE10?

To test this PR we need to do 3 things:

• Click on the Download buttons and verify the downloaded hex file is correct (looks like a normal hex file, as opposed to text or random numbers)
• In the Loda/Save modal click the the "Download Project Hex" button and confirm the hex file is correct
• In the Loda/Save modal click the the "Download Python Script" button and confirm the Python file is correct

Apart from that in Safari 6 and and 9 (but not in Safari 10!) I expect this alert to show up the file default name not to be the project name (it'll be something like "unknown" or "untitled" instead of "microbit_program"). However, the file contents should still be correct:

There were limitations to what I could check, as I couldn't open the files in safari to check them. However, the warning messages did come up for safari 9 and 6 and the files were saved as unknown. The warning didn't appear for safari 10 or IE10 and they were named microbit_program. For IE10 the files opened fine and as expected.

Thanks Josephine, I've forced the download with the alert in Safari 13 via debugger and confirm that the files work using that method.