pressing alt in full screen mode doesn't reveal menu bar; shortcuts don't work

[Scott]

using the full-screen mode entered by f11 key in lubuntu 16.04.3 LTS, with more than one tab open; similar to https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/571229 except the keyboard shortcuts don't work. e.g. alt+f, p does not open the file print option.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: firefox 56.0+build6-0ubuntu0.16.04.2
ProcVersionSignature: Ubuntu 4.4.0-97.120-generic 4.4.87
Uname: Linux 4.4.0-97-generic i686
AddonCompatCheckDisabled: False
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: scott 1044 F.... pulseaudio
BuildID: 20171003101020
Channel: Unavailable
CurrentDesktop: LXDE
Date: Sun Oct 29 08:20:08 2017
Extensions: extensions.sqlite corrupt or missing
ForcedLayersAccel: False
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
IncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
InstallationDate: Installed on 2017-09-04 (54 days ago)
InstallationMedia: Lubuntu 16.04 LTS "Xenial Xerus" - Release i386 (20160420.1)
IpRoute:
 default via 192.168.42.129 dev enp0s29f7u7 proto static metric 100
 192.168.42.0/24 dev enp0s29f7u7 proto kernel scope link src 192.168.42.100 metric 100
Locales: extensions.sqlite corrupt or missing
MostRecentCrashID: bp-0eb6939a-d128-4db2-ad12-503ff0170917
Plugins: Shockwave Flash - /usr/lib/flashplugin-installer/libflashplayer.so
PrefSources: prefs.js
Profiles: Profile0 (Default) - LastVersion=56.0/20171003101020 (In use)
RunningIncompatibleAddons: False
SourcePackage: firefox
SubmittedCrashIDs: bp-0eb6939a-d128-4db2-ad12-503ff0170917
Themes: extensions.sqlite corrupt or missing
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 05/16/2008
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A10
dmi.board.vendor: Dell Inc.
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvrA10:bd05/16/2008:svnDellInc.:pnLatitudeD620:pvr:rvnDellInc.:rn:rvr:cvnDellInc.:ct8:cvr:
dmi.product.name: Latitude D620
dmi.sys.vendor: Dell Inc.