The text takes Microsoft's Internet Explorer (6and 7), Mozilla's Firefox (2 and 3), Safari, Opera, as well as Google's own Chrome and its mobile browser, Android, and rates them against various tests and security concerns ranging from navigation to same-origin policies (rules regarding content loaded into the browser from sites other than the one currently being viewed)and plenty of in-between.
As noted in a Google blog last month, the company's rationale for making the material public -- the implication is that some or even much of this was generated for internal use, although that's not completely clear from the brief introduction -- is to "capture the risks and security considerations present for general populace of users accessing the web with default browser settings in place."
As a baseline, this is a good thing, but as the Handbook's author, Michal Zalweski notes, browsers, and particular their plug-ins and enhancements, are remarkably malleable, with many of user-added bells and whistles setting the stage for stetting off (or failing to) alarm bells and whistles when they "interfere with existing features in non-obvious ways."
Those non-obvious ways aren't the province of the Handbook as it exists now, and it will be interesting to see if the material expands to incorporate them.
Clearly written and, at first glance anyway, comprehensive, without too much of an apparent Google/Chrome-centric bias, the Browser Security Handbook is well worth a look even for non-technical staff, and more than well worth recommending to your IT team.