Originally Posted by
st1575
Did you recently upgrade to Firefox 57 and GreaseMonkey4? The Javascript error highlights one of the changes necessary to make this script work under FF57/GM4. If so, that's the problem.
As stated upthread, you can install TamperMonkey as a temporary workaround.
That's probably it. I think my FF just updated (on its own). TamperMonkey seems to work.
Thank you