Clearly not intended for API which are released in v52 and below; nightly only.
Needs a warning/experimental flag until the time that v53 is released as stable.

Do not give weight to my score: it doesn't, as expected, work on my machine but I am leaving it installed and disabled.

This extension doesn't work on my French Firefoxes 61.0.1 and 56.0.2 (both 64bit). Extension panel is empty. Have you a bug tracker?