Given the length of the code, don’t expect it to work in Internet Explorer; for what it's worth, I only tested it under Mozilla. Provided you came on that page through Google, the simplest way to test if the bookmarlet works in your browser is to click on the link above.
Credits really go to Cal Henderson, whose code I simply reduced to put it in a more suitable format for a bookmarklet. Because of the format requirements, the copyright notice isn’t include in the code itself - hopefully the following is enough:
//
// google.js
// Google Highlighter
//
// Copyright(C)2001 - 2003
// Cal Henderson <cal@iamcal.com>
//
// Thanks to Ian Beveridge for bugfixes
//
// This code may be freely redistributed,
// providing this message remains intact.
//
The code was mainly reduced by using the following command line: cat google.js |sed -e s-//.*--|tr "\r\n\t" " "|sed -e "s/ */ /g"