In your recording snippet, you'll notice a line of code like this:
window['_fs_debug'] = false;
If you switch this particular line to true, FullStory Debug mode will cause the FullStory Javascript to push an extra bundle of information to the browser console every time it runs.
This is useful for when your engineers need to troubleshoot an issue with your FullStory installation. For most of the time, we would recommend keeping debug mode false.
For example, the screenshot below shows what the browser console looks like when FS.identify is called with bad data and _fs_debug is set to true:
