Sorry, I'm not sure whether this extension works on Waterfox, but it certainly wasn't tested on it. If it says it's compatible it must be a Waterfox bug, since this site doesn't have the option to set compatibility with Firefox forks.

The latest version requires APIs only present in Firefox 57 and newer, but you could try an older version of the extension which requires an older Firefox version, and thus might work on Waterfox.