ff-disablefeatures.js

// Paste in browser console
(function() {
var s = {};
Components.utils.import("resource://gre/modules/addons/XPIProvider.jsm", s);
Components.utils.import("resource://gre/modules/addons/XPIDatabase.jsm", s);
s.XPIDatabase.getVisibleAddons(false).then(function (exts) {
    for (var ext of exts) {
        if (ext.type.indexOf("extension") > -1
            && (ext.location.name == "app-system-defaults" || ext.location.name == "app-global")) {
            s.XPIDatabase.updateAddonDisabledState(ext, true);
            console.log("Disabled " + ext.path);
        } else { console.log("Skipping " + ext.path + " (" + ext.location.name + ")"); }
    }
});
})();