I did find a solution for the flickering, my own game also uses a lot of visual. I assume it's not present in your offline version, so this is a browser issue? I have a preloader created by Avajarvis and modified by TheMadExile, it's first on the credit list here: https://docs.google.com/document/d/1751yvUabwDGyxF8K8uLeFdPdveKtrloyjyCrgQ3ryxU/...
I also use a loading screen when the game is first launched: https://twinery.org/cookbook/loadscreen/sugarcube/sugarcube_loadscreen.html