I have a set of JavaScript files in '*src*' folder compiled by Closure Compiler in a single file *cw-around.js* in '*src/comp*' with generated source maps *cw-around.js.map* also in '*src/comp*'.

"//# sourceMappingURL=xxx" is at the end of the compiled file *cw-around.js*.
xxx being a full HTTP link (local web server) to *cw-around.js.map* and being successfully tested in a browser.
{"version":3,"file":"cw-around.js" is the beginning of the *cw-around.js.map* file

In the Dev mode/sources file list, I can see the associated files in Chrome and Firefox (when I put a wrong xxx, I can see only the compiled *cw-around.js* file).

There, when I double click on an associated file (*cw-demodata.js*, one of the JavaScript file name that was included in the compiled file):

1. **In Chrome 58 or 61** ("JavaScript source maps enabled" + "source map detected"), **an empty code window is displayed**.
[![screen capture in Chrome (Windows 10)](https://i.stack.imgur.com/bAnaT.jpg)](https://i.stack.imgur.com/bAnaT.jpg)
2. **In Firefox 54** ("show original sources" + "devtools.source-map.locations.enabled;true"), **the HTML code of my calling web page is displayed**.
[![screen capture in Firefox (Windows 10)](https://i.stack.imgur.com/pEkhg.jpg)](https://i.stack.imgur.com/pEkhg.jpg)

What's wrong? How to investigate to identify what's wrong?