Comment 107 for bug 233901

duh, sorry, it uses, as you say, whatever the general.config.filename is set to.
That file needs to be plain text, unobscured, unless you you've set the obscure
pref,

general.config.obscure_value

to whatever byte offset you want to obsucre by (mozilla used to use 7 or 13,
can't remember which...)

you're probably not getting this far, but you can turn on PRLogging for MCD:

set NSPR_LOG_MODULES=MCD:5
set NSPR_LOG_FILE=c:\log.txt