See if this support article helps you:
https://support.mozilla.com/en-US/kb/Menu+bar+is+missing

Or you can open the Firefox SafeMode and use Reset toolbars and controls. Don't select anything else, just Continue in SafeMode .
http://support.mozilla.com/en-US/kb/Safe+Mode

Especially if you have hidden it yourself, the change should be simple and easy to reverse. Did you make the change by installing any new software ? if so what was it ?

Reduce the size of the viewing window so that it fits easily within the screen, just in case parts are not being seen. A re-install is a last resort, and may not even solve the problem.

Try again with using the Alt key. presumably the alt key works in other none firefox windows ?

If that is not working try firefox in safe Mode when using that do not make changes at the first dialogue Window just click the continue button. Now try the Alt key again whilst in safe mode.

If that fails then possibly a plugin or malware is causing the problem. if either of those is the reason a re-install may not necessarily help. Now work through these and see if any of them help

• troubleshooting plugins
• is my firefox problem a result of malware
• *see also Basic troubleshooting and troubleshooting extensions and themes

Thanks for your swift reply

It could indeed be a malware... safe mode was not lauching!! so i lost patience and reinstalled...still now menu bar and no adress bar and no safe mode! I downloaded vlc just before and accidentaly the billeo toolbar which could cause the issue... I think I will have some antimalware scan my pc now...

Sometimes other software is going to mess with firefox settings, something like another toolbar or search helper could do that, in which case disabling or uninstalling such software may help.

Whatever the billeo toolbar then, as you surmise, it may be the sort of software that possibly causes such problems; and may be it is worth investigating that before any further malware investigation