emacs lisp count unique items in list (elisp)

(let (items)
  (dolist (item (list ... put some list of items here ...))
    (let ((match (assoc item items)))
      (if match
          (setcdr match (1+ (cdr match)))
        (push (cons item 1) items))))

  (print items))

Vivaldi tab bar disappears by itself

It's some kind of bug and it's annoying. But turning off and on again the tab bar restores it.

In preferences you can assign a hotkey to showing the tab bar (e.g. Ctrl+Shift+A) in the view section of the hotkeys, so the disappearing tab bar can be restored with a hotkey.