Circumvents the update check for PS3's. This will make you able to use PSN with a lower PS3 firmware.
Install mitmproxy from here or from your GNU/Linux distribution.
Clone this git repository somewhere with:
git clone https://github.com/rrooij/ps3_update_proxy.git
Run the mitmproxy binary and attach this script
./mitmproxy -s tls_passthrough.py -s filereplacer.py
Note that the first time starting a game may result in a error. It will work fine if you try again by restarting the game.
Configure your computer's local IP address as proxy in the PS3, with port 8080.