Horse handles duplicate pages a little differently from other browsers. Open a page that’s already in your sidebar and Horse takes you to the existing one instead of making a second copy. Useful default, most of the time, that’s what you actually wanted.
When you do want a duplicate (you’re filling in a form on one copy and want a fresh blank version on the other, say), it’s a single shortcut.
Default: redirected to the existing page
If a page is already open somewhere in your Trail, opening it again from a link or a search jumps you to the existing one. The sidebar stays one row long instead of two.
Making a deliberate duplicate
When you want two copies of the same page, both editable independently:
Menu > File > Duplicate Trail
Keyboard shortcut
Mac: ⌘+⇧+D
Windows / Linux: Ctrl+⇧+D