Hmm... Rated 5 out of 5 stars
The programmer responded so I changed my review from 1 to 5 stars. It's always really nice to get a responce.
The options are confusing and the add-on wasted my time. I couldn't get it to copy plain text into Excel.
After all - the add-on is called "Copy As Plain Text" and not "Copy As Plain Text (Only inside Firefox)".
This add-on has been undergoing a code audit to correct some issues and to bring things up to date. Starting with v1.0.9 (which is currently available as a release candidate on the forum), the issues you have experienced should be a thing of the past.