Merci pour ta réponse lool_lauris!
voici le résultat!
henri@henri-HP-Compaq-Pro-6300-SFF:~$ killall thunderbird
thunderbird: aucun processus trouvé
henri@henri-HP-Compaq-Pro-6300-SFF:~$ thunderbird --allow-downgrade
1588548569070 addons.xpi WARN Can't get modified time of /usr/lib/thunderbird/features/
wetransfer@extensions.thunderbird.net
1588548569157 addons.xpi-utils WARN addMetadata: Add-on
wetransfer@extensions.thunderbird.net is invalid: [Exception... "Component returned failure code: 0x80520006 (NS_ERROR_FILE_TARGET_DOES_NOT_EXIST) [nsIFile.isFile]" nsresult: "0x80520006 (NS_ERROR_FILE_TARGET_DOES_NOT_EXIST)" location: "JS frame :: resource://gre/modules/addons/XPIInstall.jsm :: get :: line 235" data: no] Stack trace: get()@resource://gre/modules/addons/XPIInstall.jsm:235
syncLoadManifest()@resource://gre/modules/addons/XPIInstall.jsm:754
addMetadata()@resource://gre/modules/addons/XPIDatabase.jsm:2711
processFileChanges()@resource://gre/modules/addons/XPIDatabase.jsm:3152
checkForChanges()@resource://gre/modules/addons/XPIProvider.jsm:2946
startup()@resource://gre/modules/addons/XPIProvider.jsm:2406
callProvider()@resource://gre/modules/AddonManager.jsm:213
_startProvider()@resource://gre/modules/AddonManager.jsm:649
startup()@resource://gre/modules/AddonManager.jsm:873
startup()@resource://gre/modules/AddonManager.jsm:3470
observe()@resource://gre/modules/addonManager.js:70
1588548569159 addons.xpi-utils WARN Could not uninstall invalid item from locked install location
1588548569541 addons.xpi-utils WARN updateMetadata: Add-on
messagingmenu@mozilla.com is invalid: Error: File /usr/lib/thunderbird/extensions/
messagingmenu@mozilla.com.xpi does not contain a valid manifest(resource://gre/modules/addons/XPIInstall.jsm:671:11) JS Stack trace:
loadManifest@XPIInstall.jsm:671:11
awaitPromise@XPIProvider.jsm:228:15
syncLoadManifest@XPIInstall.jsm:755:22
updateMetadata@XPIDatabase.jsm:2822:32
updateExistingAddon@XPIDatabase.jsm:3038:23
processFileChanges@XPIDatabase.jsm:3127:31
checkForChanges@XPIProvider.jsm:2946:55
startup@XPIProvider.jsm:2406:12
callProvider@AddonManager.jsm:213:31
_startProvider@AddonManager.jsm:649:5
startup@AddonManager.jsm:873:14
startup@AddonManager.jsm:3470:26
observe@addonManager.js:70:29
1588548569543 addons.xpi-utils WARN Could not uninstall invalid item from locked install location
1588548569584 addons.xpi WARN Add-on
langpack-fr@thunderbird.mozilla.org is missing bootstrap method update
1588548569584 addons.xpi WARN Add-on
langpack-en-GB@thunderbird.mozilla.org is missing bootstrap method update
1588548569584 addons.xpi ERROR Failed to process extension changes at startup: TypeError: addon._sourceBundle is undefined(resource://gre/modules/addons/XPIDatabase.jsm:3099:32) JS Stack trace:
addonExists@XPIDatabase.jsm:3099:32
processFileChanges@XPIDatabase.jsm:3222:13
checkForChanges@XPIProvider.jsm:2946:55
startup@XPIProvider.jsm:2406:12
callProvider@AddonManager.jsm:213:31
_startProvider@AddonManager.jsm:649:5
startup@AddonManager.jsm:873:14
startup@AddonManager.jsm:3470:26
observe@addonManager.js:70:29
console.debug: "main/language-dictionaries 80 records loaded from JSON dump"
console.debug: "main/sites-classification 7 records loaded from JSON dump"
1588548608576 addons.xpi WARN Can't get modified time of /usr/lib/thunderbird/features/
wetransfer@extensions.thunderbird.net
1588548608580 addons.xpi-utils WARN addMetadata: Add-on
wetransfer@extensions.thunderbird.net is invalid: [Exception... "Component returned failure code: 0x80520006 (NS_ERROR_FILE_TARGET_DOES_NOT_EXIST) [nsIFile.isFile]" nsresult: "0x80520006 (NS_ERROR_FILE_TARGET_DOES_NOT_EXIST)" location: "JS frame :: resource://gre/modules/addons/XPIInstall.jsm :: get :: line 235" data: no] Stack trace: get()@resource://gre/modules/addons/XPIInstall.jsm:235
syncLoadManifest()@resource://gre/modules/addons/XPIInstall.jsm:754
addMetadata()@resource://gre/modules/addons/XPIDatabase.jsm:2711
processFileChanges()@resource://gre/modules/addons/XPIDatabase.jsm:3152
getNewSideloads()@resource://gre/modules/addons/XPIProvider.jsm:2982
1588548608581 addons.xpi-utils WARN Could not uninstall invalid item from locked install location
1588548608586 addons.xpi-utils WARN addMetadata: Add-on
messagingmenu@mozilla.com is invalid: Error: File /usr/lib/thunderbird/extensions/
messagingmenu@mozilla.com.xpi does not contain a valid manifest(resource://gre/modules/addons/XPIInstall.jsm:671:11) JS Stack trace:
loadManifest@XPIInstall.jsm:671:11
awaitPromise@XPIProvider.jsm:228:15
syncLoadManifest@XPIInstall.jsm:755:22
addMetadata@XPIDatabase.jsm:2711:32
processFileChanges@XPIDatabase.jsm:3152:26
getNewSideloads@XPIProvider.jsm:2982:28
1588548608586 addons.xpi-utils WARN Could not uninstall invalid item from locked install location
WebGL(0x7f31c9277000)::ForceLoseContext
WebGL(0x7f31c928a800)::ForceLoseContext
Thunderbird a démarré automatiquement juste après. J'ai du lui donner une adresse mail avec mot de passe... bref comme lorsqu'on démarre à zéro.