Thank you so much for taking the time to write such detailed and thoughtful feedback! I am definitely planning to change several things you mentioned to improve the game.
About the lags, yeah, it is several things. The browser has a poor performance in the game overall, and I am surprised it works as well as it does, never thought of it being playable in the browser to be honest, haha.
The FPS drop when going into the woods is the change between the bonfire (no dynamic shadows) and loading a lot of dynamic shadows, as you mentioned in a very tree dense zone. I will try to pace it better by loading in chunks, but it already has a lot of optimizations in place, and in the desktop version you never notice drops if you have recommended hardware to run the game, but I will take another look there for sure in what can be improved.
Also I know you are on MAC, so you can't try the desktop version. I will also take a look if I can produce a MAC version down the road, which would be cool.
Thanks again for the incredible feedback and support!