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

Other things that need attention.
See http://www.mozilla.com/plugincheck/

Your above posted system details show outdated plugin(s) with known security and stability risks that you should update.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
2. Java Plug-in 1.6.0_11 for Netscape Navigator (DLL Helper)

Update the Flash plugin to the latest version.

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

Update the Java plugin to the latest version.

• http://www.oracle.com/technetwork/java/javase/downloads/index.html (Java Platform: Download JRE)