Mozilla Firefox exists only as SNAP package :(

[deepshikas0110-cpu]

Which software package would you like that is mirrored?

Please include package X from repository Y in all Ubuntu builds ...

[igorpecovnik]

If you use our default desktop install, it pins to our repository where we provide non-snap version. Try:
apt policy firefox

It should look like this:

firefox:
  Installed: (none)
  Candidate: 152.0.5+build1-0ubuntu0.26.04.1~mt1
  Version table:
     1:1snap1-0ubuntu8 50
        500 http://archive.ubuntu.com/ubuntu resolute/main amd64 Packages
     152.0.5+build1-0ubuntu0.26.04.1~mt1 1001
        500 http://apt.armbian.com resolute/resolute-desktop amd64 Packages

You need this file:
cat /etc/apt/preferences.d/armbian-desktops

# Managed by armbian-config (module_desktops). Do not edit by hand.
#
# Force apt.armbian.com versions of these desktop packages over
# Ubuntu's snap-transitional ones. Priority 1001 is required
# (not 990) because the snap-shim packages have a higher epoch —
# 990 only allows upgrades; 1001 also permits the downgrade
# required to replace the snap-shim with the real .deb.
Package: chromium chromium-* firefox firefox-esr firefox-l10n-* thunderbird thunderbird-l10n-* google-chrome-stable code microsoft-edge-stable
Pin: release o=Armbian
Pin-Priority: 1001

# Push Ubuntu's snap-shim versions below the default 500 so they
# are never auto-selected when the real apt.armbian.com .deb is
# available.
Package: chromium chromium-* firefox firefox-esr firefox-l10n-* thunderbird thunderbird-l10n-* google-chrome-stable
Pin: release o=Ubuntu
Pin-Priority: 50