It does not work.

Anyway I would never install it in my main browser, because its code is secret and it can see all my passwords and other things that I write.

See:

https://support.mozilla.org/en-US/kb/permission-request-messages-firefox-extensions#w_access-your-data-for-all-websites

"The extension can read the content of any web page you visit as well as data you enter into those web pages, such as usernames and passwords."