(One more thing)
I managed to get to Encounter #19 when the game froze during an enemy's turn. The browser console shows "Uncaught TypeError: WebGL2RenderingContext.bufferData: Argument 2 can't be an ArrayBuffer or an ArrayBufferView larger than 2 GB". It seems like this is a Firefox-exclusive problem, but maybe there is a memory leak. I'm including a screenshot below in case the context helps.