I go through my feed or history and bg-open the links I want to watch. Then I watch them.

What a strange confusion, as if all people must have the same "workflow". Sorry, no intent to sound negative, but why not give it some thought at least. It's "6 tabs", not "6 videos playing at the same time".

As someone who hates the auto-recommendation system on YouTube and turns it off, I also appreciate this is sometimes the safest/easiest way to watch only the videos I actually intend to watch.

This seems intentionally YouTube's UX design fault, they too heavily try to push you to "auto-play". YouTube has a "Watchlist" feature where you can build a playlist. When it works it is exactly what I want, but it feels like every so many months it mysteriously breaks for a while or they hide the button for it behind some new hidden gesture or menu they expect you psychic out of their UI. (If you've never heard of "Watchlist", no wonder. It seems intentionally hard to discover.) Lately I've been complaining that YouTube adds random "auto-play" videos even to a manually curated "Watchlist" if you don't pay enough attention or watch past the end of the list (even with auto-play and recommendations entirely off).

I guess it’s not the same as Watch Later. I think I remember “add to queue” button right on videos, that was it probably.

I’m still using Watch Later, but for long videos I have no time for.

Yeah, it was named "Queue" for a while at one point. I think "Watchlist" is the most consistent name it has had, and yeah that does add (intentional?) confusion with Watch Later.

Not OP but I read it as "6 tabs" not "6 YouTube tabs."

I sometimes do have several Youtube tabs open to line up things I want to watch next.

To this, have you tried running a no-autoplay style extension? (Not exactly this scenario, but lists might be modifiable)

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.

No need – Firefox does that out of the box for tabs opened in the background (I open tabs via middle/command click)! So there is no problem for me.

We’re shifting targets here.

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.

On the internet, no one knows you have compound eyes.