Hi Gwern, I'm honestly not sure. I have some firefox extension that skips trackers and other redirects. I have like 100 firefox extensions, actually. I'm not sure how most of them work nor what they do exactly, I just trust that they make my browser more "secure" and I tend to download things at random -- especially if I see ads or want certain features in my client (i.e. a browser that auto-rejects cookies).
Happy to try and help you figure this out but when I revisit this specific hyperlink I'm still getting the gwern url & not arxiv