It's a modified/fixed version of BugMeNot by hosts
(which in terms was based on code found at http://www.oreillynet.com/pub/h/4171 )
because it didn't work anymore.
This applies in HTTP and HTTPS sites.
Many sites (e.g. online newspapers) require you to register with the site before being able to read content. This registration is annoying, invasive, and a serious privacy risk. (Several newspaper publishing companies have been caught selling their registration information to spammers.) A site called BugMeNot.com (http://www.bugmenot.com) has sprung up to aggregate fake logins for such sites. This script takes BugMeNot one step further by integrating it into the login page itself.
How to use:
After installing this script (Tools > Install This User Script), go to any page that requires Sign in.
Click on either the Username
or the Password textbox
This is what will appear:

By clicking Get login from BugMeNot
the script will contact bugmenot.com and,
if it finds a login, it will autofill the login form, as shown below:

If there were no logins found you'll get this alert box:
meaning that you can either:
- press
More Options
to open(in a new tab) the relevant bugmenot page and try(copy/paste another login), or
- just press
Visit BugMeNot
which will open(in a new tab) http://bugmenot.com .
Thanks to hosts for making a very useful script!