When using FirePHP, I ran into this issue where I could not see the output of the debug information. All the documents I found kept suggesting that I had not enabled the Console tab for this particular site.
I had done so.
Turns out, there is one other caveat: the Net tab. In addition to the console tab needing to be enabled, the Net tab also needs to be enabled for that particular site. Then, the FirePHP information comes through.