Follow the following steps-
* First of all install Greasemonkey(  Add-On to your Firefox browser.
* Click on Add to Firefox and then on install Now button.

* Now Restart your Firefox and you will see a monkey icon adjacent to your Address bar.
* After installing this you have to install a user script
Google Book Downloader(
* For this click on the install button and again on install button.

* Now you will see a message displaying Google Book Downloader installed successfully at the right bottom of your screen.
* Now go to the Google book store and find your book there.
* Here you will see a button saying Download this Book in the left panel.

* That’s it. Now you will be able read your desired book offline.

Note:- If you are not able to download book on clicking Download this Book button then install FlashGot Add-on in your browser. After installing the addon right click on the Download this Book button and select FlashGot Link option and then click start download button.