While indeed broken like other users stated, you can still use it if you fix the url it is trying to access for its interface.

The current "moz-extension://2cb62284-f1f7-4715-874d-cfab37a8af7d/popup.html is actually pointing to a folder and not a file, the one it should be pointing instead is one deeper: moz-extension://2cb62284-f1f7-4715-874d-cfab37a8af7d/popup/index.html

Opening this in a new tab restores most functionality.