The issue is mostly irrelevant for me because I’m using the default mappings alt+left/right for the navigate_backward / forward commands.
That said, in 4.3.2610291305 [beta, edge, win] I see a slightly different problem with the browser back/forward arrows. They don’t close a pane, but they do completely reload it, which is slow and makes the above commands not work anymore (apparent lost of history). I feel like just a few weeks ago, it was impressive that WF intercepted the browser back/forward commands, detected when it was back to another WF URL, and loaded that pane combo instantly, whereas now it does not.