I switched from Gnome/Unity to LXDE on my netbook because it has only 1 GB RAM. Now the Kile window has no menu bar. How does one get it back?
This does not affect all KDE applications - for example, Kate does have a menu bar.
converted comment to answer
A similar issue was reported on ubuntuforums.
In this case it was reported against Kubuntu - so the observation that you have switched to LXDE perhaps is not the key issue here.
The resolution was to rename the file
This file will then be regenerated when you next start Kile.
This will result in your own customisation settings being lost but user-defined shortcuts are retained.
Thanks to @fossfreedom for suggesting looking in
If you do not want to destroy your settings: