It's still somewhat an extra unnecessary step to lay down the squares in the beginning of each try. Doesn't the turret base function like enough for a snap position for other parts?
I don't know if even the whole zoom and pan thing is even needed. Since it was so awkward, I played completely zoomed out all the time after trying it out in the beginning. The map could be condensed a bit so it wouldn't need to be so zoomed out (for bigger sprites) and obviously having fullscreen option would help here too. And definitely moving the chest spawn point is a good idea too.
Dunno if somewhat more controlled RNG would be better. Something like maybe having 50% chance of getting part types in order like first base, then gun and finally mod before repeating. Sure it still would be random but way less likely to get snuffed out for guns for example (which is the worst). Dunno what would be considered end game but on one of my tries, I think I got a round of pretty much only ghosts and handling those with just two turrets due to their speed (and physical immunity) is not great.
In my opinion the incoming enemies text could be on the right side where effects and chances are too. It wouldn't be in the way for primary real estate for turrets (in the beginning at least) and it even is related to the information on the right side somewhat. But a button to hide it would be decent enough I guess too.
Freezing is most likely not just a mac issue since it's a browser version. Didn't come to mind to check the console for any errors though.