Daniel Lange's blog

Thunderbird in Debian stable (Bookworm) has received Thunderbird v115.3.1 as a security update.

With it comes "Supernova", a UI redesign. There is a Mozilla blogpost with a walk-through of the new UI.

Unfortunately it features a super eye-catching "New Message" button that - thankfully - can be disabled. Even the whole space above the email folder pane can be recovered by disabling the folder pane header at Burger Menu (☰) -> View -> Folders -> Folder Pane Header.

Unfortunately there is no way to remove the same eye-catching "New Event" button for the Calendar view via a UI setting.

This needs a user CSS file to override the button as non-visible.

To make it process the user CSS Thunderbird needs a config setting to be enabled:

1. Burger Menu (☰) -> Settings -> General
2. Scroll down all the way
3. Click the Config editor... button on the bottom right
4. Accept that hell will freeze over because you configure software
5. Search for toolkit.legacyUserProfileCustomizations.stylesheets
6. Toggle the value to true to enable the user CSS

You can manually add user_pref("toolkit.legacyUserProfileCustomizations.stylesheets", true); to ~/.thunderbird/abcdefgh.default/prefs.js to the same effect (do this while Thunderbird is not running; replace abcdefgh with your Thunderbird profile ID).

Now create a new directory ~/.thunderbird/abcdefgh.default/chrome/, again replacing abcdefgh with your profile ID.

Inside the new directory create a userChrome.css file with the following content:

Restart Thunderbird. And enjoy less visual obstruction when using the Calendar.

The font size Mozilla chose for Firefox and Thunderbird menus looks awfully large on Netbook screens. It wastes space and is visually at odds with reasonably sized content. And for some weird reason you can set the content font and size via the menu but not the font and size for the drop-down menus themselves.

As the "Theme Font & Size Changer" Add-On doesn't work reliably and phones home way too often (showing a nag screen), I dug back into how to do this "manually". Probably a decade after I fixed this the first time...

You need to create the file ~/.mozilla/firefox/*/chrome/userChrome.css with * being your profile directory (<random_number>.default usually) and you most probably have to create the chrome directory first.

The same for Thunderbird resides in ~/.thunderbird/*/chrome/userChrome.css. Here again the chrome directory will most probably need to be created first.

needs to go into these files for Firefox or Thunderbird respectively. The curly braces are important. So copy & paste correctly. Symlinks or hardlinks are fine if those files do not need to differ between your web browser and your email client.

Restart Firefox and/or Thunderbird to see the effect.

Obviously you can choose any other font and font size in the snippet above to suit your taste and requirements.

If you are massively space-confined and don't mind a quite ugly UI, check out the Littlefox Add-on. Ugly but optimal use of the minimal screen estate with very small screens.