The news of the time interval is that Mozilla is selling out Firefox users once again (although Firefox remains far better than Chrome), in the form of 'Privacy-Preserving Attribution', which you might impolitely call 'browser managed tracking'. Mozilla enabled this by default in Firefox 128 ( cf ), and if you didn't know already you can read about how to disable it here or here . In the process of looking into all of this, I attempted to find where in the Firefox code the special dom.private-attribution.submission.enabled was actually used, but initially failed. Later, with guidance from @mcc's information , I managed to find the code and learned something about how Firefox handles certain 'about:config' preferences through a system called 'StaticPrefs'.

The Firefox source code defines a big collection of statically known about:config preferences, with commentary, default values, and their types, in modules/libpref/init/StaticPrefList.yaml (reading the comments for preferences you're interested is often quite useful). Our dom.private-attribution.submission.enabled preference is defined there. However, you will search the Firefox source tree in vain for any direct reference to accessing these preferences from C++ code, because their access functions are actually created as part of the build process, and even in the build tree they're accessed through #defines that are in StaticPrefListBegin.h . In the normal C++ code, all that you'll see is calls to 'StaticPrefs:<underscore_name>()', with the name of the function being the name of the preference with .'s converted to '_' (underscores), giving names like dom_private_attribution_submission_enabled. You can see this in dom/privateattribution/PrivateAttribution.cpp in functions like ' PrivateAttribution::SaveImpression() ' (for as long as this source code lives in Firefox before Mozilla rips it out, which I hope is immediately).

(In the Firefox build tree, the generated file to look at is modules/libpref/init/StaticPrefList_dom.h.)

Some preferences in StaticPrefList.yaml aren't accessed this way by C++ code (currently, those with 'mirror: never' that are used in C++ code), so their name will appear in .cpp files in the Firefox source if you search for them. I believe that Firefox C++ code can also use additional preferences not listed in StaticPrefList, but it will obviously have to access those preferences using their preferences name. There are various C++ interfaces for working with such preferences, so you'll see things like a preference's value looked up by its name, or its name passed to methods like nsIPrincipal's 'IsURIInPrefList()'.

A significant amount of Firefox is implemented in JavaScript. As far as I know, that JavaScript doesn't use StaticPrefs or any equivalent of it and always accesses preferences by their normal about:config name.