Investigate greprefs.js as it pertains to our Firefox runs in WebPageTest

Just a note that once we're looking at tooling reliability/coverage, etc., to take a look at https://searchfox.org/mozilla-central/source/modules/libpref/greprefs.js (along with other prefs, as they are used via WebPageTest).

#include ../../security/manager/ssl/security-prefs.js
#include init/all.js
#include ../../devtools/shared/preferences/devtools-shared.js
#ifdef MOZ_DATA_REPORTING
#include ../../toolkit/components/telemetry/datareporting-prefs.js
#endif
#ifdef MOZ_SERVICES_HEALTHREPORT
#if MOZ_WIDGET_TOOLKIT != android
#include ../../toolkit/components/telemetry/healthreport-prefs.js
#endif
#endif