Right-click on a Tab to see that menu item.

Found it! Thanks!

Some menu entries in the main menu bar are hidden if you use the mouse and only appear if you use the keyboard to open the menu (Bug 626825).

You can see the difference if you use Alt+F to open the File menu or other menus like the Edit menu (Alt+E) and Bookmarks menu (Alt+B) and compare that to what you see if you use the mouse to open the menu after you have made the menu bar visible by tapping Alt or by pressing F10.

• "Bookmark All Tabs" (Shift+Ctrl+D) no longer shows in the Bookmarks menu unless you open the Bookmarks menu via the keyboard (Alt + B).
• "Bookmark All Tabs" can be accessed via the right-click context menu of a tab on the tab bar.