firefox displays menu mnemonics by default

[Marc Deslauriers]

GTK applications hide the menu mnemonics by default, but firefox doesn't.

It should, else it looks like ass.

This is possibly a dupe of bug 597825.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: firefox 57.0.1+build2-0ubuntu0.17.10.1
ProcVersionSignature: Ubuntu 4.13.0-19.22-generic 4.13.13
Uname: Linux 4.13.0-19-generic x86_64
AddonCompatCheckDisabled: False
ApportVersion: 2.20.7-0ubuntu3.6
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/pcmC0D0p: mdeslaur 2160 F...m pulseaudio
 /dev/snd/controlC0: mdeslaur 2160 F.... pulseaudio
BuildID: 20171129230227
Channel: Unavailable
CurrentDesktop: ubuntu:GNOME
Date: Wed Dec 13 11:00:47 2017
ForcedLayersAccel: False
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
IncompatibleExtensions:
 English (South Africa) Language Pack - <email address hidden>
 Français Language Pack - <email address hidden>
 English (GB) Language Pack - <email address hidden>
 Default - {972ce4c6-7e08-4474-a285-3208198ce6fd}
InstallationDate: Installed on 2017-12-12 (1 days ago)
InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Release amd64 (20171018)
Plugins: Shockwave Flash - /usr/lib/adobe-flashplugin/libflashplayer.so (adobe-flashplugin)
PrefSources: prefs.js
Profiles: Profile0 (Default) - LastVersion=57.0.1/20171129230227 (In use)
RelatedPackageVersions: adobe-flashplugin 1:20171212.1-0ubuntu0.17.10.1
RunningIncompatibleAddons: True
SourcePackage: firefox
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 09/27/2017
dmi.bios.vendor: LENOVO
dmi.bios.version: N1MET39W (1.24 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20HRCTO1WW
dmi.board.vendor: LENOVO
dmi.board.version: SDK0J40709 WIN
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.modalias: dmi:bvnLENOVO:bvrN1MET39W(1.24):bd09/27/2017:svnLENOVO:pn20HRCTO1WW:pvrThinkPadX1Carbon5th:rvnLENOVO:rn20HRCTO1WW:rvrSDK0J40709WIN:cvnLENOVO:ct10:cvrNone:
dmi.product.family: ThinkPad X1 Carbon 5th
dmi.product.name: 20HRCTO1WW
dmi.product.version: ThinkPad X1 Carbon 5th
dmi.sys.vendor: LENOVO