The fact is, it doesn’t happen in Chrome for “magical” reasons, according to a comment few levels up. And regular non-tech users won’t debug this with click to play or whatever. We expect that YT does it absolutely intentionally.
It bends userbases however it wants due to its multi-dimensional reach, and we’re like “hmm maybe extension would help prevent accidental preloading issue”. I just don’t get it.
I expect YT is probably doing some preloading or heavyweight running in a loaded-but-not-playing tab.
Convert that to load-on-click, and you'll likely fix your issue.