This is the Firefox book I was looking for. Topics are grouped by task (installation, security, web development, xml tools) and everything I was curious about in Firefox was explained somewhere in the book. Missing Firefox features are pointed out (xml validation, for instance) and workarounds suggested by platform. The only thing I spotted as notably absent was the popular Greasemonkey extension, which allows a user to customize web pages. It was a very small omission - I guess none of the topics needed to reference it.
I rate the book an 9 out of 10. Outstanding job.