Oh no that's a horrendous memory leak!!
I actually noticed it a while ago and worked to resolve it, which I thought I did. I wonder if other people are experiencing it..
Either way, thanks for reporting the issue and I'll take a look as soon as I'm home from my short holiday. So probably in the next week.
Your other notes and feedback align with a lot of other feedback we've gotten and we've got some ideas to address it for the main game. The only issue is the pausing when you leave the browser window.. I think that's a browser constraint that might be tricky to work around. Will take a look at it anyways.
Glad you enjoyed it. We've got a rough plan of the content we're aiming for in the main game and I hope its substantial enough!!