The add-on is working fine, but every time Fx starts (I am using 58 Nightly and Windows) a yellow alert appears across the top of the page warning that it is slowing down Fx and asking if I want to stop or remove it - but this alert also disappears too quickly for me to select any of those options! Not that I would.
I believe this is due to the manner in which the extension listens for changes to the DOM. It's a bit of heavy code, but generally runs fast. I'll try out a few different approaches and see if I can get away with Firefox not throwing the slow extension warning. Thanks for bringing this to my attention.
