Rated 1 out of 5 stars
I'm tired of the issues of incompatibility with the most recent versions of FIrebug, that way, i've given up FirePHP and I found one better alternative: FireLogger, which uses its own in Firebug and have much configuration options. https://addons.mozilla.org/en-US/firefox/addon/firelogger/This review is for a previous version of the add-on (0.6.2.1-signed).
Compatible versions are posted at: http://www.firephp.org/
The latest version will appear here once it passes the addon approval process.
You can use DeveloperCompanion on the client as an alternative: http://developercompanion.com/