The extension works on www.reddit.com not old.reddit.com

Does what it says. There are literally people in these reviews failing two sentence long guidelines and instructions.

Thank you to the author.

Does not function as advertised. Have used for many years on chrome but will be switching for firefox.

Just hide sidebar but don't save wasted space, and it should be better to put the button at reddit pages rather than toolbar, just to do such a simple thing.

Windows 10 1803, Firefox Developer Edition 62.0b12 (64bit)
Other Installed Extension for Reddit: RES (Reddit Enhancement Suite), Reddit Comment Collapser.