All UXP-Hardened-Preferences packages also known as
icedove-uxp-hardened-preferences are being removed as we have added custom firejail profiles for
each UXP application.
about:config options were useful prior to
our transition to UXP, when
we did not have control over
upstream (Mozilla) sources.
As we have been implementing the features directly into our applications, these
left-over hacks are no longer needed.