Have you upgraded from an earlier Firefox, or did you do a clean install?

Updated from the last version. Using Firefox automatic update.

Click on the menu icon in the right top corner, then on bottom right button named customize thereafter below approximately in the middle se show/hide toolbars here in drop-down menu, choose turn on the menu bar.

Not really very helpful. "Click on the menu icon in the right top corner" does not produce anything, so the rest of your answer is not helpful.

Also click on the three-striped button nothing happens? In this case should try to clean install of Firefox.

Right-click in the upper part of the toolbar area and find the Customize menu item.

Sounds like you may have an incompatible add-on.

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

(If you're using an added theme, switch to the Default theme.)

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu by clicking on the Restart with Add-ons Disabled... menu item:


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)

Once you get the pop-up, just 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.

Problem appeared when "Default Full Zoom Level" extension was installed.