Thunderbird 115 how to set date display and fonts

After recent Thunderbird UI updates, a basic UI ‘feature’ went away: showing full date everywhere. Instead it was using 3:45 - and I need to copy and paste this as an actual date.
Thought I would share a solution.

This will make Thunderbird 115 show the Message Thread pane: with Date Column:

  • Text set Font to fixed width.
  • Date/time to be displayed as iso date time [yyyy-mm-dd tu 21:46]

In Thunderbird 115:

  1. Set advanced preference to use legacy stylesheets:
    a) Edit|Settings (or Tools|Preferences)|General|Indexing (bottom, right side)
    b) click Config Editor
    c) search: toolkit.legacyUserProfileCustomizations.stylesheets
    d) below the results list (if any), select the row, click Boolean, click + sign.
    e) set toolkit.legacyUserProfileCustomizations.stylesheets = true

  2. Set the Date text formatting: (optional). In advanced preferences:
    a) intl.date_time.pattern_override.date_short (string) =yyyy-MM-dd eeeeee
    b) intl.date_time.pattern_override.connector_short (string) = {1} {0}

  3. Create a ./chrome/userChrome.css file below the active Thunderbird profile directory:
    a) Help|Troubleshooting Information
    b) Application Basics|Profile Directory|click Open Directory
    c) Opens a file manager window to:
    /home/auser/.thunderbird/randomchars.default/
    d) If chrome/ folder not present in folder, create the chrome/ folder:
    /home/auser/.thunderbird/randomchars.default/chrome/
    e) Create/save the userChrome.css in the folder, with this content:
    /home/auser/.thunderbird/randomchars.default/chrome/userChrome.css
    settings used:

/* In the message Thread pane: table rows: Date Column: Set Font to fixed width */
#threadTree table[is="tree-view-table"] > tbody > tr > td.datecol-column
{
    appearance: none !important;
    font-family: "Driod Sans Mono",monospace !important;
}
  1. Close Thunderbird.

  2. Start Thunderbird.

[1] Customize Date and Time formats in Thunderbird | Thunderbird Help
[2] Unicode Locale Data Markup Language (LDML) Part 4: Dates
[3] Customize Date and Time formats in Thunderbird | Thunderbird Help
[4] Unicode Locale Data Markup Language (LDML) Part 4: Dates
[5] font-family - CSS: Cascading Style Sheets | MDN