Sometimes toolbars are missing because they are hidden, you can right click on top and check Menu Bar and also you can customize this.

It's NOT that the toolbar is missing-- it is that there are items missing under the Firefox menu. I can't customize anything because the Preferences item is missing and the Cmd-, shortcut does not work.

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

Safe Mode did not restore the missing items in the Firefox menu.

After starting FF in Safe Mode and not seeing any changes I re-started FF in normal mode and the missing Firefox menu items have reappeared. Thanks Sukanta Pal and the-edmeister!

I just updated my previously installed Firefox 38.0.1 to 38.0.5 on a Mac running on 10.6.8 (Snow Leopard), and experienced the exact same problem when Firefox relaunched. Immediately looked here for information and was glad to see this thread.

Restarting in Safe Mode did not restore the missing items in the Firefox menu for me either, but then they reappeared after I quit Firefox and relaunched it normally. Very odd problem that I have never seen before in all the years I've been using Firefox, but I'm glad it was so easy to resolve the issue. Thanks chetgw for posting your query about this problem!