This says it works with Firefox 48.0 or later, it doesn't.
I use Firefox 52.9 ESR on my old Windows XP machine, and the current version updated fine there but doesn't work, there's an extension icon but it doesn't do anything. Version 20.3.10 doesn't seem to work either. The last version which does still seem to still work in Firefox 52.9 is 20.2.501.
Please update your Firefox version requirements as it's misleading people at the moment!
Works great on the current Firefox versions on Windows 10 of course.