thunderbird unwarrantly pastes context info

[Humphrey van Polanen Petel]

When copying some text into a thunderbird email, context information is added as well (see attached).
<Ctrl-Z> will delete the text proper, but not the context information.
--
Version:1.0 StartHTML:0000000277 EndHTML:0000024342 StartFragment:0000022201 EndFragment:0000024302 SourceURL:file:///Y:\us\Humphrey\Articles\Constructing%20Aristotle's%20categories\How%20to%20derive%20Aristotle’s%20categories%20from%20First%20Principles%20-16.02.docx
--

In order to only paste the text proper, one needs to "paste without formatting".

This is not intuitive.

Please fix.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: thunderbird 1:78.7.1+build1-0ubuntu0.20.04.1
ProcVersionSignature: Ubuntu 5.8.0-44.50~20.04.1-generic 5.8.18
Uname: Linux 5.8.0-44-generic x86_64
AddonCompatCheckDisabled: False
ApportVersion: 2.20.11-0ubuntu27.16
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: humphrey 287754 F.... pulseaudio
BuildID: 20210203182138
CasperMD5CheckResult: skip
Channel: Unavailable
CurrentDesktop: Unity:Unity7:ubuntu
Date: Fri Mar 5 17:55:20 2021
DefaultProfileExtensions: extensions.sqlite corrupt or missing
DefaultProfileIncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
DefaultProfileLocales: extensions.sqlite corrupt or missing
DefaultProfilePrefErrors: Unexpected character ',' before close parenthesis @ /usr/lib/thunderbird/omni.ja:greprefs.js:732
DefaultProfilePrefSources: prefs.js
DefaultProfileThemes: extensions.sqlite corrupt or missing
ExecutablePath: /usr/lib/thunderbird/thunderbird
ForcedLayersAccel: False
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 # Include files from /etc/network/interfaces.d:
 source-directory /etc/network/interfaces.d
InstallationDate: Installed on 2021-01-14 (50 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
IpRoute:
 default via 192.168.0.1 dev eno1 proto dhcp metric 100
 default via 192.168.1.1 dev wlx001325ad55e1 proto dhcp metric 600
 169.254.0.0/16 dev wlx001325ad55e1 scope link metric 1000
 192.168.0.0/24 dev eno1 proto kernel scope link src 192.168.0.10 metric 100
 192.168.1.0/24 dev wlx001325ad55e1 proto kernel scope link src 192.168.1.103 metric 600
MostRecentCrashID: bp-d8ee9043-ef35-483e-8c89-c1b0d0181224
Profile1Extensions: extensions.sqlite corrupt or missing
Profile1IncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
Profile1Locales: extensions.sqlite corrupt or missing
Profile1PrefErrors: Unexpected character ',' before close parenthesis @ /usr/lib/thunderbird/omni.ja:greprefs.js:732
Profile1PrefSources: prefs.js
Profile1Themes: extensions.sqlite corrupt or missing
Profiles:
 Profile1 - LastVersion=68.10.0/20200629235513 (Out of date)
 Profile0 (Default) - LastVersion=78.7.1/20210203182138 (In use)
RunningIncompatibleAddons: False
SourcePackage: thunderbird
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/14/2020
dmi.bios.release: 2.48
dmi.bios.vendor: HP
dmi.bios.version: N01 Ver. 02.48
dmi.board.name: 8054
dmi.board.vendor: HP
dmi.board.version: KBC Version 05.39
dmi.chassis.type: 4
dmi.chassis.vendor: HP
dmi.ec.firmware.release: 5.57
dmi.modalias: dmi:bvnHP:bvrN01Ver.02.48:bd07/14/2020:br2.48:efr5.57:svnHP:pnHPEliteDesk800G2SFF:pvr:rvnHP:rn8054:rvrKBCVersion05.39:cvnHP:ct4:cvr:
dmi.product.family: 103C_53307F G=D
dmi.product.name: HP EliteDesk 800 G2 SFF
dmi.product.sku: L1G76AV
dmi.sys.vendor: HP