Right side of window and menu area is duplicated every time on first run

[Wes]

Every time I open Firefox with previous session tabs the first time right after logging in, the usable portion of the window is shrunk, and the right side of the window with the last tab, menus, and extension icons is duplicated on the right side of the window. (See screenshot)

Closing and reopening Firefox almost always fixes the issue. I may have had this happen once on a non-first run after resuming.

Started happening recently I think in 62.0.3

Expected: Window opens normally.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: firefox 63.0+build2-0ubuntu0.18.04.2
ProcVersionSignature: User Name 4.15.0-38.41-generic 4.15.18
Uname: Linux 4.15.0-38-generic x86_64
AddonCompatCheckDisabled: False
ApportVersion: 2.20.9-0ubuntu7.4
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: ubuntu 1745 F.... pulseaudio
 /dev/snd/controlC0: ubuntu 1745 F.... pulseaudio
BuildID: 20181023214826
Channel: Unavailable
CurrentDesktop: ubuntu:GNOME
Date: Fri Nov 2 10:55:29 2018
DefaultProfileExtensions: extensions.sqlite corrupt or missing
DefaultProfileIncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
DefaultProfileLocales: extensions.sqlite corrupt or missing
DefaultProfilePrefSources: prefs.js
DefaultProfileThemes: extensions.sqlite corrupt or missing
EcryptfsInUse: Yes
ForcedLayersAccel: False
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
InstallationDate: Installed on 2018-09-12 (50 days ago)
InstallationMedia: Ubuntu 16.04.5 LTS "Xenial Xerus" - Release amd64 (20180731)
IpRoute:
 default via 192.168.1.1 dev wlp3s0 proto dhcp metric 600
 169.254.0.0/16 dev wlp3s0 scope link metric 1000
 192.168.1.0/24 dev wlp3s0 proto kernel scope link src 192.168.1.224 metric 600
MostRecentCrashID: bp-5252eef0-71dd-4e49-8315-64d660180929
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
Profile1Extensions: extensions.sqlite corrupt or missing
Profile1IncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
Profile1Locales: extensions.sqlite corrupt or missing
Profile1PrefSources: prefs.js
Profile1Themes: extensions.sqlite corrupt or missing
Profiles:
 Profile0 (Default) - LastVersion=63.0/20181023214826 (In use)
 Profile1 - LastVersion=62.0/20180913170346 (Out of date)
RunningIncompatibleAddons: False
SourcePackage: firefox
SubmittedCrashIDs:
 bp-5252eef0-71dd-4e49-8315-64d660180929
 bp-57477e57-d8dd-4ea9-ba66-270d80180929
 bp-821e4afc-cb3c-4fe2-a7ba-586440180929
 bp-8b4ffe0f-54ef-4969-b8fa-7d6bd0180929
UpgradeStatus: Upgraded to bionic on 2018-09-28 (34 days ago)
dmi.bios.date: 07/09/2018
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A17
dmi.board.vendor: Dell Inc.
dmi.chassis.type: 9
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvrA17:bd07/09/2018:svnDellInc.:pnLatitude3340:pvr00:rvnDellInc.:rn:rvr:cvnDellInc.:ct9:cvr:
dmi.product.name: Latitude 3340
dmi.product.version: 00
dmi.sys.vendor: Dell Inc.

[Wes (wesinator)]

Happened again, this time when opening firefox right after gnome-terminal was opened and moved to the right side of the screen. The terminal window portion can be seen in the firefox window area.

Dragging and remaximising Firefox fixed the window.