https://support.mozilla.com/en-US/kb/Restore+the+default+Smart+Bookmarks+Folders

Thanks alot. That worked, but there is still one thing missing. There was an arrow at the top and bottom of the bookmarks window, so I could scroll up and down. That also disappeared when I deleted one of the default bookmarks, and it didn't come back when I just did the above.

"... arrow at the top and bottom of the bookmarks window ..."

Window? The "Library" window has scroll bars on the right-side is each panel.
If you are talking about the Bookmarks drop-down from the Menu bar, the "scroll" buttons only appear when that drop-down is taller than the browser window. Those "arrows" can't be deleted like the Smart folders can.

You're right. Duh, sorry to waste your time!