To be fair, if the problem is the amount of data that will travel through your connection, there is not much difference between this and a 120MB text-only html file.
So maybe browsers should offer a setting to cap the data retrieved from each individual domain on metered connections, unless instructed otherwise on a domain-by-domain basis?
This is only problem on fast and capped connections which I would guess are rare. On slow connection (and proper browser) you see that it's downloading data, how much, how fast and you can stop it.
Oh, you are right. I was under the impression that 4G is something like 2-3 Mbps, which would make the caps somewhat proportional and hard to pass by accident. But I just tried speedtest.net (app) and download speed was almost 40 Mbps. I really had no idea.
So maybe browsers should offer a setting to cap the data retrieved from each individual domain on metered connections, unless instructed otherwise on a domain-by-domain basis?