@Samizdata I seem to be able to keep the federated timeline from scrolling down by doing this:

highlight the text of some post, then scroll down a bit and read posts underneath (timeline is not moving on its own now), scroll back up and read newer ones; if I scroll all the way back to the top it carries on in the usual fashion, pushing posts down.

This is in Chrome on octodon.social with a little experimentation after I noticed that sometimes I was able to read the timeline without it moving.