I can confirm this bug, and it also happens in the Save As dialog that opens when you press Ctrl+S. I tried downgrading Firefox to 151.0.4-1 and this makes the issue go away.
I tried analyzing this a bit with ChatGPT and found that the Save button in the Save As dialog and the Open button in the Open File dialog can still be activated by Alt+S and Alt+O respectively, so it's not a focus issue. According to ChatGPT, this suggests that the dialog response associated with GTK_RESPONSE_ACCEPT is not activated by Enter anymore.
