I use Win7, Firefox 56.0.2 64 bits (please don't ask why). I must say that I use Dark reader for a long time and was quite happy (5 stars) until Version 4.9.35.

The (latest) version (4.9.37.1) does not work either on Win7+Firefox 56.0.2 64 bits (sorry I need this config). It displays "loading in progress ..." (or something like that) and that's it.

Uninstalled and replaced by the previous version (4.9.34) (thanks to https://addons.mozilla.org/fr/firefox/addon/darkreader/versions/) works. Except that on the next load the automatic extensions update replaces it by the (last ) version. For now I have removed the automatic extensions update, not a big deal, rare are the extensions that update w/ my config ;)

All works properly now \o/ I just stopped to upgrade above 4.9.34.