To disable the menu bar in konqueror, you have a specific action in menus. If you want to do this by hand, just add the following directive in your ~/.kde/share/config/konquerorrc file:

[KonqMainWindow]
MenuBar=Disabled

This tip is interesting because you can also apply it for any KDE application that doesn’t support this feature.

For example, in kmail, you can add the “MenuBar=Disabled” statement in “[Main Window]” section: this will have the same effect as in konqueror.