Adds fields for persistent global & fandom filters to works index pages on AO3
Yes, it seems like Greasemonkey is very poorly supported in 57. But, Tampermonkey runs on 57, so switch to that.
So I deleted Greasemonkey, installed Tampermonkey, then ran/installed your script, and voila, the saved filters were back. Is it really that simple? If so, bless you!
Firefox 57.0 update
Just updated my Firefox to v57.0 and this script has completely disappeared! :(