Cannot create a launch.json file

VSCode refuses to let me choose Firefox when clicking the "create launch.json" link in the run page.

Is there any way to fix that appart from open vim and manually creating the file?

Start from the VS Code Run page and the "create launch.json" link, reproducing the failure when choosing Firefox. Trace the launch.json creation flow and verify that selecting Firefox creates a usable file instead of refusing the action.

Written by the indexing model from the issue text.