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

I've already tried all those things and they didn't help. Any other ideas?

I found I had to exit Full Screen Mode to get my recently disappeared toolbars back. See this link: https://support.mozilla.org/en-US/kb/what-happened-to-the-file-edit-and-view-menus

This may have been caused by the Rel. 39 update that Mozilla pushed out on Thursday, which was automatically applied to my system. I check my Advanced Options. Update was set to "Automatically install updates". I always try to have this set to "Check for updates, but let me choose". Mozilla has overridden this before and changed my preference. If that's what happened here I am really irked.

You did verify that you are no longer in full screen mode (Mac: Command+Shift+F).?

• https://support.mozilla.org/kb/how-to-use-full-screen

Try to rename (or delete) the xulstore.json file in the Firefox profile folder.

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox