A quick howto:

1. Right click on a password box with password entered into it by a password manager or another user and select "Inspect element". If right mouse button is disabled - press F12 and try again.
2. Make a note of id="xxx" property on the input tag
3. In the address bar type (case sensitive):
   

   javascript:alert(document.getElementById('xxx').value);
   

   Where xxx is the name identified in step 2.

You should see the alert window displaying the hidden password.