waterfox.
Have tried chrome, but while that works, it momentarily shows the fail message when the game starts. (but that could simply be an artifact from how loading is handled and it resolves on its own in a blink of an eye)
Viewing post in Existential Crisis Simulator. comments
Yeah, the 'uh oh something broke' message is intentionally displayed by default until the game data loads (because if it doesn't load, that means that something has gone wrong).
I've never used Waterfox myself, but I guess that there's something weird in that browser that doesn't like this hypertext game framework. But I'm glad that you were eventually able to play it.