Olá,

1. Vá até a pasta do seu perfil:
   • Perfis
   • Profile folder
2. Feche completamente o Thunderbird.
   • http://kb.mozillazine.org/Kill_application
3. Procure pelo arquivo prefs.js.
4. Abra o arquivo prefs.js com um editor de texto, por exemplo, o Bloco de Notas.
5. Procure pela seguinte linha.
   • user_pref("font.name.monospace.x-western", "CSD10");
6. Note que "CSD10" não deve ser o nome de uma fonte do seu arquivo prefs.js
7. Apague esta linha e salve o arquivo.
8. Reinicie o Thunderbird.
9. Veja mais:
   • http://kb.mozillazine.org/Corrupted_message_body_display

Ou você pode tentar criar um novo perfil

A linha ' user_pref("font.name.monospace.x-western", "CSD10"); ' não existe. Por isso, não resolve meu problema.

O Thunderbird já está atualizado na última versão.

Segue conteúdo do prefs.js desta parte

user_pref("extensions.lastAppVersion", "24.6.0"); user_pref("extensions.lastPlatformVersion", "24.6.0"); user_pref("extensions.pendingOperations", false); user_pref("extensions.shownSelectionUI", true); user_pref("extensions.ui.dictionary.hidden", true); user_pref("extensions.ui.lastCategory", "addons://discover/"); user_pref("extensions.ui.locale.hidden", true); user_pref("font.internaluseonly.changed", true); user_pref("font.name.monospace.el", "Consolas"); user_pref("font.name.monospace.tr", "Consolas"); user_pref("font.name.monospace.x-baltic", "Consolas"); user_pref("font.name.monospace.x-central-euro", "Consolas"); user_pref("font.name.monospace.x-cyrillic", "Consolas"); user_pref("font.name.monospace.x-unicode", "Consolas"); user_pref("font.name.monospace.x-western", "Consolas"); user_pref("font.name.sans-serif.el", "Calibri"); user_pref("font.name.sans-serif.tr", "Calibri"); user_pref("font.name.sans-serif.x-baltic", "Calibri"); user_pref("font.name.sans-serif.x-central-euro", "Calibri"); user_pref("font.name.sans-serif.x-cyrillic", "Calibri"); user_pref("font.name.sans-serif.x-unicode", "Calibri"); user_pref("font.name.sans-serif.x-western", "Calibri"); user_pref("font.name.serif.el", "Cambria"); user_pref("font.name.serif.tr", "Cambria"); user_pref("font.name.serif.x-baltic", "Cambria"); user_pref("font.name.serif.x-central-euro", "Cambria"); user_pref("font.name.serif.x-cyrillic", "Cambria"); user_pref("font.name.serif.x-unicode", "Cambria"); user_pref("font.name.serif.x-western", "Cambria"); user_pref("font.size.fixed.el", 14); user_pref("font.size.fixed.tr", 14); user_pref("font.size.fixed.x-baltic", 14); user_pref("font.size.fixed.x-central-euro", 14); user_pref("font.size.fixed.x-cyrillic", 14); user_pref("font.size.fixed.x-unicode", 14); user_pref("font.size.fixed.x-western", 14); user_pref("font.size.variable.el", 17); user_pref("font.size.variable.tr", 17); user_pref("font.size.variable.x-baltic", 17); user_pref("font.size.variable.x-central-euro", 17); user_pref("font.size.variable.x-cyrillic", 17); user_pref("font.size.variable.x-unicode", 17); user_pref("font.size.variable.x-western", 17); user_pref("idle.lastDailyNotification", 1405939116); user_pref("intl.charsetmenu.mailview.cache", "windows-1252, UTF-8, ISO-8859-1"); user_pref("ldap_2.servers.ContatosApenasestecomput.description", "Contatos (Apenas este computador)"); user_pref("ldap_2.servers.ContatosApenasestecomput.dirType", 2); user_pref("ldap_2.servers.ContatosApenasestecomput.filename", "impab.mab"); user_pref("mail.account.account1.identities", "id1"); user_pref("mail.account.account1.server", "server1"); user_pref("mail.account.account2.server", "server2"); user_pref("mail.account.account3.server", "server3"); user_pref("mail.account.lastKey", 3); user_pref("mail.accountmanager.accounts", "account1,account2,account3"); user_pref("mail.accountmanager.defaultaccount", "account1"); user_pref("mail.accountmanager.localfoldersserver", "server2"); user_pref("mail.append_preconfig_smtpservers.version", 2); user_pref("mail.attachment.store.version", 1); user_pref("mail.biff.play_sound", false); user_pref("mail.biff.show_alert", false); user_pref("mail.biff.show_tray_icon", false); user_pref("mail.compose.attach.dir", "C:\\Users\\diego.panisson\\Desktop"); user_pref("mail.displayname.version", 1121); user_pref("mail.folder.views.version", 1); user_pref("mail.font.windows.version", 2); user_pref("mail.identity.id1.archive_folder", "imap://[email protected]/Archives"); user_pref("mail.identity.id1.attach_signature", true); user_pref("mail.identity.id1.doBcc", false); user_pref("mail.identity.id1.draft_folder", "imap://[email protected]/INBOX/Rascunhos"); user_pref("mail.identity.id1.drafts_folder_picker_mode", "1"); user_pref("mail.identity.id1.encryptionpolicy", 0); user_pref("mail.identity.id1.fcc_folder", "mailbox://nobody@Local%20Folders/Enviados"); user_pref("mail.identity.id1.fcc_folder_picker_mode", "1"); user_pref("mail.identity.id1.fullName", "Diego Panisson - Gerente Geral de Vendas"); user_pref("mail.identity.id1.reply_on_top", 1); user_pref("mail.identity.id1.sig_file", "S:\\Assinaturas\\Comercial\\Diego.html"); user_pref("mail.identity.id1.sig_file-rel", "[ProfD]../../../../../../../../S:/Assinaturas/Comercial/Diego.html"); user_pref("mail.identity.id1.sign_mail", false); user_pref("mail.identity.id1.smtpServer", "smtp1"); user_pref("mail.identity.id1.stationery_folder", "imap://[email protected]/Templates"); user_pref("mail.identity.id1.tmpl_folder_picker_mode", "0"); user_pref("mail.identity.id1.useremail", "[email protected]"); user_pref("mail.identity.id1.valid", true); user_pref("mail.last_msg_movecopy_target_uri", "imap://[email protected]/INBOX/Ranking Cadastro"); user_pref("mail.openMessageBehavior.version", 1); user_pref("mail.pane_config.dynamic", 2); user_pref("mail.phishing.detection.enabled", false); user_pref("mail.preferences.advanced.selectedTabIndex", 3); user_pref("mail.preferences.compose.selectedTabIndex", 0); user_pref("mail.purge_threshold_migrated", true); user_pref("mail.rights.version", 1); user_pref("mail.root.imap", "C:\\Users\\diego.panisson\\AppData\\Roaming\\Thunderbird\\Profiles\\cv9l4diz.default\\ImapMail"); user_pref("mail.root.imap-rel", "[ProfD]ImapMail"); user_pref("mail.root.none", "C:\\Users\\diego.panisson\\AppData\\Roaming\\Thunderbird\\Profiles\\cv9l4diz.default\\Mail"); user_pref("mail.root.none-rel", "[ProfD]Mail"); user_pref("mail.server.server1.ageLimit", 30); user_pref("mail.server.server1.applyToFlaggedMessages", false); user_pref("mail.server.server1.cacheCapa.acl", true); user_pref("mail.server.server1.cacheCapa.quota", true); user_pref("mail.server.server1.check_new_mail", true); user_pref("mail.server.server1.cleanupBodies", false); user_pref("mail.server.server1.daysToKeepBodies", 30); user_pref("mail.server.server1.daysToKeepHdrs", 30); user_pref("mail.server.server1.directory", "C:\\Users\\diego.panisson\\AppData\\Roaming\\Thunderbird\\Profiles\\cv9l4diz.default\\ImapMail\\diferrowall.diferro.com.br"); user_pref("mail.server.server1.directory-rel", "[ProfD]ImapMail/diferrowall.diferro.com.br");

Reinicie o Thunderbird com os complementos desabilitados (Modo Thunderbird Seguro). No menu Ajuda, clique em "Reiniciar com os complementos desativados". Se o Thunderbird funciona normal, há um problema com algum complemento ou tema. Você vai precisar reativar os complementos, um de cada vez, até localizar o infrator.

Reiniciei o Thunderbird com os complementos desabilitados (Modo Segurança) e mesmo assim, o problema continua. Ao Encaminhar emails, não aparece o corpo da mensagem que desejo encaminhar.