Comment 71 for bug 23369

In my testing, it does NOT work.
When setting config.use_system_prefs the settings you listed become "locked", and the firefox network dialog becomes grayed out.
The settings from gconf is however not used, in about:config e.g. type is 0 (no proxy) and the various host fields are blank.

I have tried to get debug info using
export NSPR_LOG_FILE=/tmp/firefox-debug.log
export NSPR_LOG_MODULES="all:5"
firefox

but the only mention of system-pref is:
-1221551264[805c548]: Loaded library /usr/lib/firefox/components/libsystem-pref.so (load lib)

Currently compiling firefox with DEB_BUILD_OPTIONS=debug to see if that makes any difference to the debug output.