A JavaScript conflict is one thing they're looking at...
I pulled up developer console in Chrome and Firefox earlier today. Had no obvious issues in Chrome, but it pulled about 15MB in a minute hitting a Google video site among multiple requests.
On Firefox, in one minute it pulled about 60MB hitting the same Google video sites and had serious lag issues.
Enabling AdBlock Plus on each had Chrome pulling about 15k in a minute and FF pulling about 50k in a minute. This cleared up the lag issues, so it seems to be the ads causing issues on my machine.
I meant to send this earlier today, but work got in the way. I can provide more detail tomorrow if necessary. On a side note, I've had to keep re-posting this response multiple times because parts of it keep getting lost and/or mangled. This is an iPad using Tapatalk.
...Another edit because things keep getting lost: I was using a Dell XPS 15 with 32GB RAM and a 4-core i7 running Windows 10.