Hello Christoph.
This post is related to issue #29 (
http://code.google.com/p/firephp/issues/detail?id=29). This is a workaround, your json_encode method is disabled and I'm using PHP's build-in json_encode().
After unpacking archive point your browser to 2 examples:
public/example_dibiphp.php
public/example_mdb2.php
Example_dibiphp.php is using promising db layer dibi (
http://dibiphp.com) and example_mdb2.php is using PEAR's MDB2 (
http://pear.php.net/package/MDB2). This handler looks promising, hope that someone will find it usefull. Looking forward to your own json_encode working from the scratch. There are some minor modifications in FirePHP.class.php, just avoiding E_NOTICE messages and disabling json_encode method. Patch is included in archive.
FirePHP_with_errorHandler.tar.gz