Can't install CKEditor footnotes plugin on 4.13

[LiquidFractal]

After reinstalling the custom buttons on my editor after the most recent CKEditor upgrade, I find I cannot install the CKEditor Footnotes plugin - it craps out with "invalid plugin," even though I've been using the same plugin for years.  Even re-downloaded it fresh from the site but no luck.

Is there a way to try to finagle the button in by uploading the un-zipped files?  Or is there something else I can do?

Thanks!