It's hard to explain what I'm trying to figure out, so please bear with me. Let's say I've scrolled a long way down my twitter feed, and there's a post whose replies I want to read. I click to be taken to that tweet's page. Now, if, on that second page, I see another post I'd like to read replies to, I click on that to be taken to the third tweet's page. My question is how do I get back to the original tweet that was halfway down my feed, without being taken to the very top of my twitter feed, where I have to start scrolling all over? I've searched FAQs and watched youtube videos, and nowhere can I find an answer to this.
That's the "beauty" of an infinite scroll. Even using the browser's back button is not going to take you back to the exact spot.
Greasemonkey (Firefox), Tampermonkey (Chrome), .. - w/o modifying the default behavior (by editing JS), you won't be able to do that.
But it's not an infinite scroll problem because you haven't gone back to the feed yet. I don't think there's an answer for generic twitter but it's worth researching the user scripts libraries (eg GreasyFork) to see what's there and what works for you.