Firefox fails to start up and displays XML Parsing Error: undefined entity

[Karl Kastner]

Firefox does not start up, instead a window opens that shows:

XML Parsing Error: undefined entity
Location: chrome://browser/content/browser.xul
Line Number 1165, Column 7: <menuitem class="pageActionContextMenuItem extensionUnpinned"
------^

Removing the ~./mozilla folder does not help. Version is 58.0+build6-0ubuntu0.17.10.1
This report is filed using Waterfox instead.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: firefox 58.0+build6-0ubuntu0.17.10.1
ProcVersionSignature: Ubuntu 4.13.0-29.32-generic 4.13.13
Uname: Linux 4.13.0-29-generic x86_64
AddonCompatCheckDisabled: False
ApportVersion: 2.20.7-0ubuntu3.7
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: pia 3276 F.... pulseaudio
 /dev/snd/controlC0: pia 3276 F.... pulseaudio
BuildID: 20180122225545
Channel: Unavailable
CurrentDesktop: GNOME
Date: Sat Jan 27 14:27:52 2018
Extensions: extensions.sqlite corrupt or missing
ForcedLayersAccel: False
IncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
InstallationDate: Installed on 2015-11-05 (814 days ago)
InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
IpRoute:
 default via 10.75.15.254 dev eth0 proto static metric 100
 10.75.0.0/20 dev eth0 proto kernel scope link src 10.75.0.58 metric 100
 169.254.0.0/16 dev eth0 scope link metric 1000
Locales: extensions.sqlite corrupt or missing
Plugins: Shockwave Flash - /usr/lib/gnash/libgnashplugin.so (browser-plugin-gnash)
PrefSources: prefs.js
Profiles: Profile0 (Default) - LastVersion=58.0/20180122225545 (In use)
RelatedPackageVersions: browser-plugin-gnash 0.8.11~git20160608-1.3
RunningIncompatibleAddons: False
SourcePackage: firefox
Themes: extensions.sqlite corrupt or missing
UpgradeStatus: Upgraded to artful on 2018-01-16 (11 days ago)
dmi.bios.date: 04/15/2014
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 4.6.5
dmi.board.asset.tag: Tag 12345
dmi.board.name: W230SS
dmi.board.vendor: Notebook
dmi.board.version: Not Applicable
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 9
dmi.chassis.vendor: Notebook
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr4.6.5:bd04/15/2014:svnNotebook:pnW230SS:pvrNotApplicable:rvnNotebook:rnW230SS:rvrNotApplicable:cvnNotebook:ct9:cvrN/A:
dmi.product.family: Not Applicable
dmi.product.name: W230SS
dmi.product.version: Not Applicable
dmi.sys.vendor: Notebook

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.