Wouldn't it be a good idea to take the loggerpack made by trabis and integrate it to 2.4.2? I just copied over the old files from 2.3x and they still work and it makes debugging far easier. Only drawback at the moment: you have to configure in the configs file.
Unzip it, backup the two files in class/logger (render.php and xoopslogger.php) and copy the content of the unzipped loggerpack in there. Open xoops_data/configs/xoopsconfig.php in an editor and change this:
legacy -> normal XOOPS debug firephp -> debugger for Firefox, addons firebug and firephp have to be installed pqp -> PHP Quick Profiler
Now visit Preferences | General Settings and pick up "Enable debug (inline mode) from setting Debug Mode. Hit "Go" and you are done.
Drawback for firephp: at some places you might get a blank page. Especially when file operations are involved. An exception is thrown which firephp is not capable to resolve. But this one is my favourite, because your layout is destroyed by debug information and at the same time, you get all information.