There are some onion sites I want to keep track of but the URLs are so long. Is using pinned tabs and bookmarks a secure option? Will people be able to track me if I set bookmarks or pin some tabs?
About Internet security and anonimacy: You're almost safe, unless NSA cracks into your computer to spy your Bookmarks and session files.
About Computer being secure: You're not safe, since you are leaving tracks on your hard disk about which sites do you visit.
So if your computer has any risk of being seized by NSA, FBI, Communist Party of China, Guardians of the Revolution, or your mother, do not use Bookmarks nor pinned tabs. On the other hand, if you feel you are locally safe, do whatever you wish.