Thank you! Some extensions might provide extra functionality which might require a very general permission to make it work, I don't know, but this one was designed to be very lightweight and simple.

I used a gray icon because I wanted the menu item to look like it was part of the browser as much as possible. Unfortunately, WebExtensions require an icon to be shown on the menus, which is the same as the extension's icon. So, unless I changed the extension's icon to a blank one, the menu option also needs to have one.

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.

Can you please clarify what doesn't work? Which Firefox version and platform are you trying to use this extension on?