Very good addon if you want to manage cookie exceptions. But unfortunately with the latest Firefox update (version 42) it does not work anymore. The cookie exceptions list is always displayed blank. After disabling the addon, the exceptions list works again. Hope this bug will be fixed. Like "bredmond" I find no other contact info for the author.
Unfortunately this does not seem to be a simple fix. There have been a couple changes made in v42 (most obviously "Save Changes" instead of immediate changes) but I can't pin down why the list of permissions isn't appearing in the first place. What I've done now is lowered the max version of my extension to v41.*. I know this wasn't the news you were hoping for :(
However, I have put the source code up on GitHub, so you (or anyone else) are welcome to contribute (hopefully a fix) via pull request.