Update on my earlier reply:
Can you please confirm what version of Firefox you tried to use to play the game and/or if it’s a “release” rather than “development”/“nightly”/etc version?
After some investigation I think the error may be related to the itch.io “Origin Trial” token having expired but due to an Firefox implementation detail this may only stop release versions from working (thus why I hadn’t encountered the issue as I was using a Firefox development build).
Thanks again for your feedback.
[I’ve alerted itch.io to the possible issue here: https://itch.io/t/2025776/experimental-sharedarraybuffer-support#post-9707481]