Firefox - "Open posts in new tab" works but also opens the post in the main tab

On Firefox 145.0.2 only (not in Chrome 142.0.7444.176) on Mac OS, I have "Open posts in new tab" turned on in my preferences. Starting today, clicking a post opens a new tab with the post, but at the same time, sets the original tab to open the post too (instead of staying in my feed, which it used to).

In Chrome, it still works correctly: click a post, it opens in a new tab, and the original tab stays where it was in my feed.