Some of you may have found that FirePHP doesn’t work after upgrading to Firefox 6.
It appears that in Firefox 6.0.2 + Firebug 1.8.2, FirePHP 0.6.2 (Firebug extension) isn’t appending “FirePHP/0.6” to the browser’s User Agent request headers. This is the case wven when the “Modify User Agent headers” option is turned on.
The missing “FirePHP/0.6” in the User Agent string causes the FirePHP server library to NOT respond with the appropriate X-Wf-* headers.
The quick solution for now is to install and run FirePHP/Firebug in a portable version of Firefox 5. It worked for me.
I’ve also posted this issue to the FirePHP bug tracker: Issue 177
Update
The other way around it is to start with a fresh Firefox profile using the Firefox Profile Manager
