Armbian: improve APT pinning for Firefox/Thunderbird

- Change Pin from origin domain to release origin for more reliable pinning
- Improve comments to clarify priority behavior (1001 prevents downgrades)
- Add explanatory comments for Ubuntu repository deprioritization
- Fix typo in upstream comment

This ensures Firefox and Thunderbird are consistently installed from the
Armbian repository with proper pinning rules.

Author: igorpecovnik

packages/bsp/common/etc/apt/preferences.d/armbian

@@ -1,4 +1,13 @@
-# Install those packages rather from Armbian repo
+# Force installation of these packages from Armbian repository
+# Priority 1001 forces Armbian's version even if it requires downgrading
+# a currently installed version from another repository
+# Ubuntu snap versions have higher epoch version
 Package: firefox firefox-esr thunderbird
-Pin: origin apt.armbian.com
-Pin-Priority: 700
+Pin: release o=Armbian
+Pin-Priority: 1001
+
+# Deprioritize Ubuntu versions to avoid conflicts
+# Priority 50 ensures Ubuntu packages are not selected when Armbian versions exist
+Package: firefox firefox-esr thunderbird
+Pin: release o=Ubuntu
+Pin-Priority: 50