separate tabs in safari

FIrefox allows one to add a separator between Favorites items. Safari used to, but has removed that capability, and now, there is no user interface, or secondary menu item to allow separators to be added by the user. There must be remnant code in Safari that remains to purposely honor Firefox bookmark separators only on import.

One could rename their Safari favorites on the toolbar and reformat them as "| bookmark |" using the U+007C Vertical Line character.

If you are asking about the sites listed just below the URL box, you can't add a separation bar. If that isn't what you mean, more information would help.

The lines may be associated with the Firefox Bookmarks. I have never seen vertical lines in the Favorites Bar when using Safari Bookmarks.