New Jellyfin installation - CBZ images not displayed

[huntrrz]

Jellyfin version: Ubuntu 10.8.10
Install method: curl https://repo.jellyfin.org/install-debuntu.sh...
Client: Ubuntu Firefox 116.0.3
Log file: New Thread page tells me 'The type of file you attached is not allowed...' ???

Problem: 

CBZ contents displayed as 'broken image' icon, but browser advances pages back and forth

Notes:

Machine dual boots OS X El Capitan and Ubuntu, accessing same partitions (I'm migrating to Ubuntu)
Scanned existing Calibre library on HFS+ partition
Located story in CBZ format, EPUB format in same folder
EPUB contents displayed correctly through web browser

Guesses on cause:

Missing plug in?
Missing utility app?
Improper permissions?