> The solution I use is to set media.autoplay.blocking_policy to 2 in about:config (I found this on the Mozilla wiki [1]). This setting requires a click to play media.

Not really. The mozilla wiki says:

>The technical detail for this policy is that the play invocation should be triggered inside an user input event handler.

If the autoplay is what OP described (ie. "starting to auto-play just by scrolling into view"), then that would satisfy the condition because it's within an user input event handler (the scroll).