This feature can be found on version 91 and there you may spot a new section on the new tab view. It shows tiles for websites that you added to bookmarks recently. The Show all button next to this section will also navigate you to your bookmarks view.
How to test:
- Open any webpage on Firefox.
- Tap on the 3 dots menu to open options.
- Add page to bookmarks.
- Tap on the new tab button.
- Check a new Recently saved section.