Works flawlessly, didn't even know it worked until I checked the resulting file.
It saves the conversion as .webp.jpg in downloads automatically, no questions.
The double file extension might get buggy or troublesome on Windows if you have hide file extensions enabled by default. In that case, you will just see .webp in the Windows explorer folder repeatedly and I bet someone will say it didn't work because of that.
When you get a one-star review that says something like that, just know I called it out in advance. User error, not the add-on.
Ten oudda ten, quick, silent, no extra steps needed. Now if you want terrible formats, could you do one like this for avif files 🤣 I see Mozilla is trying to push their own original format too and I don't know if it's worse or better than webp at this point.