• If, on Windows, in Firefox 3.6 the menu bar is hidden then press and hold the Alt key down or press F10, that should make the "Menu Bar" appear
• Go to "View > Toolbars" and check-mark "Menu Bar" with a click on it to make that permanent. See Restore the Menu bar in Firefox).
• Make sure that you have the "Navigation Toolbar" and the "Bookmarks Toolbar" visible: "View > Toolbars"
• If items are missing then see if you can find them in the "View > Toolbars > Customize" window
• If you see the item in the Customize window then drag it back from the Customize window onto one of the toolbars.
• If, in "View > Toolbars > Customize", you do not see that item then click the "Restore Default Set" button

See http://kb.mozillazine.org/Toolbar_customization

Thanks for the response to my question. I had just found the same solution myself, but I appreciate your help.

You're welcome

Yes, the reply here (forgot the replier's name, sorry) is excellent and solved it for me. But Mozilla really needs to study what is wrong here! For two days I could not use Firefox at all. I uninstalled it and reinstalled it hoping that something had been corrupt in my version. No dice. I COULD NOT right-click on ANY PART of the area at the top of the page to get the usual list of bars that I want. NO, that did not produce a drop-down no matter where I clicked. So the advice to hold the Alt key down was the only thing which saved me . . . I could not go to Tools or View or even Help because that bar was also missing. Firefox, you really need to make sure this does not happen to anyone, it is serious! I was using Google Chrome and IE for two days and dissatisfied with both. And who in the world would guess that holding the Alt bar down would fix it???

Rungrin‘s solution works ,she has a wonderful technical mind, so thanks to her and thank you too .