But it only works if you have access to the box the password is stored on, because the user has to put the code into the url bar while the filled password input field is visible.
If you're at someone else's comp and for some reason feel the need to read their pw, it's propably easier to either look at the pw manager, or open the browser dev tool and change the input type from password to text.
By the way, for that reason it's smart to use a master pw if you're storing passwords in your browser.
