This article describes the major changes that are visible to users in Thunderbird version 52.0. Full details of all the changes can be found in the Thunderbird 52 release notes.
Compared to Thunderbird version 45.0, it has far less visible changes to the user interface but instead, many long-standing bugs and annoyances were fixed.
Table of Contents
The most important change is how images are included in a compose window. Images are now included as data URIs and not as references to parts of other messages or operating system files. This allows better interoperability with office packages such as MS Office or LibreOffice. It also fixes long-standing problems with attaching images from other messages. Images linked from locations on the Internet will no longer be downloaded and attached to the message automatically. This can be changed for each image individually via the Image Properties dialog or globally by setting the preference mail.compose.attach_http_images.
Since data URIs are basically raw binary data displayed in the user interface, these are now shortened in the Image Properties dialog and the Insert HTML dialog, for example:
When pasting images that reference operating system files into the compose window, the image will now be blocked and a notification will be displayed:
This is to protect users from inadvertently disclosing files.
Main Message Window - Folder Pane
The folder pane now has a Folder Pane Toolbar on the top which comes preconfigured with the Folder Views switcher. The Folder Pane Toolbar can be enabled through the View menu > Toolbars.
Main Window - Thread Pane
The Correspondents column with new icons is now the default for all new folders. There is no forced conversion. This can be switched off with the preference mail.threadpane.use_correspondents.
Calendar - Lightning - Event in a Tab
Events can now be created and edited in a tab. To enable this option, select ToolsEditThunderbird menu > OptionsPreferences > Calendar > General tab.in the