can’t establish a connection to the server at localhost:8096

[mineymo]

Hello all and thank you in advance for any help you might be able to give.

Jellyfin 10.8.13
Installed from MacOS .dmg

I'm using Jellyfin via Firefox and playing from media stored on 2 external hard drives. The iMac is connected to the TV via HDMI. Jellyfin has only ever been used by me on that single iMac which 95% of the time is not connected to the internet.
I've been using Jellyfin for well over a year now without any issues. It's been great. However, for the last few days, upon clicking the Jellyfin logo in the taskbar, rather than being brought to the Jellyfin splash page and then my media library, i get "Unable to connect
Firefox can’t establish a connection to the server at localhost:8096."
I don't know what I've done to cause this behaviour or what has changed. Any thoughts greatly appreciated. Most recent logs here: https://pastebin.com/2hFHEN25

[theguymadmax]

You upgraded to version 10.9.z, encountered a database issue, and then downgraded to 10.8.13. Once you upgrade to 10.9.z, you cannot downgrade to 10.8.z due to database incompatibility.

Please check for a backup of your database at this location:
/Users/imac/.local/share/jellyfin/data/
Look for files with a *.bak* extension:
library.db.bak*

If you find the backup, ensure the server is shut down. Then, rename the files as follows:
- Rename library.db to library.db.old
- Rename library.db.bak* to library.db

Then restart the server.