Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that turns off some settings, disables most add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• In Firefox 29.0 and above, click the menu button , click Help and select Restart with Add-ons Disabled.
• In previous Firefox versions, click on the Firefox button at the top left of the Firefox window and click on Help (or click on Help in the Menu bar, if you don't have a Firefox button) then click on Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

Thanks for your reply. I already did as you suggested, using the Safe Mode, but I was still unable to add anything to the Bookmarks toolbar.

Do you still see any bookmarks on the Bookmarks Toolbar?

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

It worked.....thank you so much!!!