Firefox 3.6+ versions have a feature to allow the user to hide the Menu bar.

Hit the Alt key to temporarily show the Menu bar, then open View > Toolbars and select Menu bar, so it has a check-mark.
The F10 can also be used on most PC's to temporarily reveal the Menu bar.

https://support.mozilla.com/en-US/kb/Menu+bar+is+missing

There are other things that need attention:

Your above posted system details show outdated plugin(s) with known security and stability risks that you should update.

1. Shockwave Flash 10.1 r85

Update the Flash plugin to the latest version.

• http://www.adobe.com/software/flash/about/