As soon as I posted this question, FF Support immediately showed me the same question in older posts: 1. https://support.mozilla.org/en-US/questions/1278303 2. https://support.mozilla.org/en-US/questions/1264371 Both have replies marked as solutions, but they don't work consistently for the OPs or for me. I've tried making sure to have opened the window on the external monitor before opening a link - that didn't work. I've tried exchanging the windows between the laptop and the monitor - the laptop's window still opens. Those posts were 4/5 years old. Does this mean that FF now has a solution? Thanks so much. ge