Yes! Quantum is just a code name for all the big and exciting improvements happening in Firefox 57. None of your personal data will be lost in the update.

niccity said

If I migrate from FF 56 to Quantum will bookmarks, history and saved passwords be carried over?

You will have to login again at any site you saved passwords at, but that will not be a problem. Browsing history and bookmarks are saved.

The Saved Passwords Button is now missing and there isn't a replacement! Especially if we used this to remember the passwords with. WHY do you call this an improvement when you take away things we use? Other Add-Ons missing that I want back are the Roomy Bookmarks Toolbar and Undo Closed Tab Button.... Thank you.