Actually in my experience Firefox CSP debugging is light years ahead of Chrome's. Not only debugging - CSP in Firefox at least works as intended, while with Chrome(ium) it's hit and miss. [0]

That said, it does happen that Firefox gives a cryptic error message, and running in Chromium gives enough clues to solve the problem. But usually FF is much better with CSP, at least in my experience (and I work with CSP pretty often).

[0] EDIT: "miss" meaning that the request, forbidden by CSP rules, is not stopped. Firefox correctly stops the same request.