Base64 encoded images/emotes drawn out of topic bounds

[Sebastian "Nait" Kacprzak]

Image in topic is draw out of bounds. This did not happen in Thunderbird from 17.10 (attached: base64Topic.png, HugeEmoteInTopic.png)

I think the relevant part of eml file is:

Subject: =?utf-8?B?8J+RiSBGb3Rva3NpxIXFvGthIDIxIHggMjgganXFvCBvZCAx?=
 =?utf-8?B?MzUgesWC?=
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: base64

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: thunderbird 1:52.7.0+build1-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-15.16-generic 4.15.15
Uname: Linux 4.15.0-15-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
AddonCompatCheckDisabled: False
ApportVersion: 2.20.9-0ubuntu5
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: nait 1917 F.... pulseaudio
 /dev/snd/controlC1: nait 1917 F.... pulseaudio
BuildID: 20180416164209
Channel: Unavailable
CurrentDesktop: ubuntu:GNOME
Date: Tue Apr 17 11:50:04 2018
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 2017-10-18 (180 days ago)
InstallationMedia: Ubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
IpRoute:
 default via 192.168.1.1 dev wlp9s0 proto dhcp metric 600
 169.254.0.0/16 dev wlp9s0 scope link metric 1000
 192.168.1.0/24 dev wlp9s0 proto kernel scope link src 192.168.1.108 metric 600
Locales: extensions.sqlite corrupt or missing
PrefSources: prefs.js
Profiles: Profile0 (Default) - LastVersion=52.7.0/20180416164209 (In use)
RunningIncompatibleAddons: False
SourcePackage: thunderbird
Themes: extensions.sqlite corrupt or missing
UpgradeStatus: Upgraded to bionic on 2018-04-17 (0 days ago)

[Launchpad Janitor (janitor)]

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