The first time I click the "Dual Lister" toolbar button after starting Directory Opus, it always displays the two listers side-by-side (*commander mode) instead of top and bottom. I prefer top and bottom because my monitor is in portrait orientation. I can get it there by clicking the "=" button in the lister title bar (for lack of a better name), and it will remember that's how I want to see dual listers for the rest of the Directory Opus session, but if I close Directory Opus or reboot, it forgets. Can I somehow make this setting persist across sessions?
Your suggestion causes Opus to open in dual lister mode by default, which isn't exactly what I want. Most of the time I browse in single lister mode. But when I do enable dual listers, I would like them to show top and bottom. I tried different variations on the theme and I still couldn't get it working.
The F6 hotkey is tied to the toolbar button for toggling dual display mode, so you just need to edit that button, as per Jon's message above.
Alternatively, you can find it via Settings > Customize Toolbars > Keys (or Help > Keyboard Map, which goes to the same place) and looking for F6 under the Toolbars section of the list.
(You can also push F6 on the filter at the bottom of the dialog to see just the hotkeys involving F6, to find it quickly.)