Thanks, that helps a lot!
You were right about the souls: each one was drawn separately, so a late game screen full of them (plus March of the dead) cost a lot. In the next update all souls are drawn in one go, and the march is lighter too.
The double click on “Next” / “Got it” was a real bug as well, also fixed in the next update.
I’ll test it on Firefox too.
Thanks for giving it another go, let me know how it runs :)