Script Summary: Add a link to every amazon link that points to a product lookup
Whenever you encounter a link to a book on Amazon, this script will strip out the ISBN and append it to a search url (right now it is Google Shopping, but this is easy to change).
A small text-icon appears to the upper-right of the original link, and this link will take you to the search page.
It is easy to change the search page and the text of the icon. Theoretically you could make a copy of this script and add an icon for each kind of search you would like to do for any Amazon URL.