How to download books from Google books for Free?

 Here is the trick to download google book and read it off line also. 

How to do this?
Step 1:
Download/install Greasemonkey addon(Customize the way a web page displays or behaves, by using small bits of JavaScript.) in Firefox

Install this userscript :google book download

Download/insall the Flashgot (FlashGot is the free add-on for Firefox and Thunderbird, meant to handle single and massive