Works great on FF Nightly 55 (2017-05-29), except for some small nuances, like the "Export to zip" not working, and unlike Tampermonkey it is open-source.
More smaller than Tampermonkey + under permissive license. Greasemonkey on this moment not supported webextension-api and must be rewrited from scratch for support Firefox 57+ (as of many other extensions).
