That jetpack builds an unique and strong password for each web site you visit.
It combines a master password (never stored) with the web page location hashed by SHA1 and transformed to ASCII characters.
A checkbox allows you to choose if the generated password may contain specials characters or only plain text (number, lower and upper case letters).
You will find that Jetpack on the Mozilla Jetpack gallery.
The source code contains a suite of unit tests written using QUnit.
That jetpack includes a SHA1 script from Chris Veness. Many thanks !