See:

• https://support.mozilla.org/kb/how-do-i-use-bookmarks

In current Firefox releases (29 and later), that have have the Australis user interface, the orange Firefox menu button has been replaced by the three-bar Firefox Menu button at the far right end of the Navigation Toolbar and this button is always visible, whether you have the menu bar visible or hidden
A consequence of this location is that you no longer can hide the Navigation Toolbar

• There is a star like button next to the search bar on the Navigation Toolbar to bookmark the current web page and a "Show your bookmarks" button next to it to open the Bookmarks in a drop down menu.
  You can find "Show All Bookmarks" to open the Bookmarks Manager (Library) at the bottom of this drop-down list
• If you bookmark a page then "Bookmark This Page" in the Bookmarks menu changes to "Edit This Bookmark"
• You can make the title bar visible via the "Title Bar" button at the bottom left in the Customize palette window

It is still possible to have the menu bar visible via the right-click context menu of a toolbar to have menus like the File menu with Print (Ctrl+P) and Print Preview and the Bookmarks menu available.

See also:

• https://support.mozilla.org/kb/how-to-make-new-firefox-look-like-old-firefox
• https://support.mozilla.org/kb/common-questions-after-updating-to-new-firefox
• https://support.mozilla.org/kb/learn-more-about-the-design-of-new-firefox

The term "Manage Bookmarks" hasn't been used in Firefox for 8 or 9 years now, Organize Bookmarks replaced it until Firefox 4 when it became Show All Bookmarks.

When you select Show All Bookmarks the Library window opens. Then use Import and Backup > Export bookmarks to HTML ... and save that file to a Flash drive.

Then your grandson can use Import bookmarks from HTML .... to add that file of your bookmarks to his own bookmarks.

Note that using the Backup feature would result in a file that would overwrite another persons bookmarks when they would "restore" that file.