So I don't have this bug in HTML5 on the crit's page, but I do occasionally get this:
Yet, as mentioned before, I am able to finish the creating of the ritual with dragging the error icons.
As seen on this screenshot not every flash module in this page has crashed. Sometimes they all do, sometimes less.
This is on xubuntu 18.04, Firefox 64.0
but since it's not consistent in the result I will put my bet in the latest Flash update, which in my system is from early December, and I haven't noticed this issue in the previous months.