This is not a HPH issue (I have disabled HPH and checked, it still happens) but this is a thread that the webdevs might see. I'll DM the devmods as well and link to this.

Since the downtime yesterday, if I open a thread view in the queue and then mouse over a quote reply link, the quote reply appears behind the thread view popup, instead of in front of it. Here's an example where you can see the quoted post sticking out to the side.

on firefox, in case it matters