Safari: How do I show history in a new tab in Safari?
As neither way to access history [from menu or from a toolbar button] allows you to open it in a new tab by the usual method of  Cmd ⌘   Shift ⇧  clicking I'd suggest the best method might just be open it in a manual new tab - 2 keystrokes. 


 Cmd ⌘   T   for new Tab  
 Cmd ⌘   Y   for History


Apparently, Show History  Cmd ⌘   Y  may not be the same key command in all Languages, but I can only check for UK English...