I went ahead and also fixed the deltamodeScreen because it's simple. I tested all modes on windows and linux with chrome and firefox

Also while writing this patch, I noticed that the line

// touchpads can give ev.deltaY == 0, which skrews the lvl calculation
if (ev.deltaY === 0) return

is no longer necessary (the new formula doesn't divide by zero in this case, it keeps the same zoom level), do you want me to remove it in another PR ? it simplifies the code and makes its behavior more homogeneous

Nice code and comment :)

do you want me to remove it in another PR

Yes please - that line can go