I use a 4K monitor as my main monitor, with my laptop off to one side. Nearly every app I open opens correctly on the 4K monitor.
But Firefox always opens on the laptop monitor, even when its windows were on my 4K monitor when closed. Also, when I make a new window in Firefox, it opens on the laptop monitor (even when all existing Firefox windows are in the 4K monitor). Needless to say, this is very annoying.
How can I configure Firefox (or my Mac OS) to correctly open new windows on the 4K monitor like all other apps do?
This is on Mac OS 10.11.6 and Firefox 78.1.0esr.