In your data capture snippet, you'll notice a line of code like this:
window['_fs_script'] = 'edge.fullstory.com/s/fs.js'
window['_fs_script'] = 'edge.fullstory.com/s/fs-debug.js';
This is useful for when your engineers need to troubleshoot an issue with your FullStory installation. For most of the time, we would recommend using the default script.
For example, the screenshot below shows what the browser console looks like when FS.identify is called with bad data and the debug version is being used: