Initially just look the customise options, have you moved the bookmarks icon ? By default it is alongside the searchbar not underneath it.

• Customize Firefox controls, buttons and toolbars

You may be able to find it and put it back where you want it.

Next if that did not help try the Firefox Refresh (reset).

Note that will remove Firefox extensions so make a note of them and their homesites before you reset.

• See Refresh Firefox - reset add-ons and settings
  The article actually has an active button to initiate the reset.

Do NOT delete the copy profile that is created, it may have data needed to recover bookmarks.

Make sure that toolbars like the "Bookmarks Toolbar" are visible.

• "3-bar" Firefox menu button > Customize > Show/Hide Toolbars
• View > Toolbars
  Tap the Alt key or press F10 to show the Menu Bar
• Right-click empty toolbar area

Open the Customize window and set which toolbar items to display.

• "3-bar" Firefox menu button > Customize

• check that "Bookmarks Toolbar items" is on the Bookmarks Toolbar
• if "Bookmarks Toolbar items" is not on the Bookmarks Toolbar then drag it back from the Customize palette into the Customize window to the Bookmarks Toolbar

• if missing items are in the Customize palette then drag them back from the Customize window on the toolbar
• if you do not see an item on a toolbar and in the Customize palette then click the Restore Defaults button to restore the default toolbar setup

• https://support.mozilla.org/kb/customize-firefox-controls-buttons-and-toolbars

You can check for problems with the places.sqlite database file in the Firefox profile folder.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox
• https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

• Places Maintenance: https://addons.mozilla.org/firefox/addon/places-maintenance/