From MozillaZine Knowledge Base

This article applies to both Thunderbird and the Mozilla Suite.

Changing the display format for today's date

By default the Mozilla Suite and Thunderbird display the time only (without the date) for messages less than one day old.  For messages older than this, both the date and time will be displayed.  To change the display format for today's date, exit the Mozilla Suite or Thunderbird and insert the following line into the "user.js" file, replacing [value] with one of the values shown in the table below:

user_pref("mail.ui.display.dateformat.today", [value]);

* Some operating systems have only one date format. On these systems, the values 1 and 2 produce the same result.

Example:

user_pref("mail.ui.display.dateformat.today", 2);

With the above line inserted into user.js, messages received or sent during the current day will be displayed with both the date and time. The date will be in your operating system's current short date format (which is typically a numeric format).

You can also edit the configuration using about:config or the Thunderbird Config Editor.

Changing the display format for other dates

You can similarly change the display format for "this week" (the past seven days excluding today) or the default date format (all dates excluding the past seven days). To do so, use one of the values shown in the table above and insert the appropriate line of code into the "user.js" file, as shown below.

For "this week":

user_pref("mail.ui.display.dateformat.thisweek", [value]); 

For the default date:

user_pref("mail.ui.display.dateformat.default", [value]);

Configuring the date/time system settings on your computer

In addition to the settings shown above, the precise display formats for date/time can also be affected by the system settings for date/time on your computer. For instance, depending on your computer's system settings, the numerical display format for the date could be "31.12.1999", "1999/12/31", "12/31/1999", or something else.

In Windows XP, you can change the settings for date/time format by going to the Control Panel. See here for detailed instructions.

In Linux, these settings are based on your locale. If the environment variable "LANG" is set to "en_US", for example, Thunderbird will show the date in "MM/DD/YYYY" format. To override the locale only for showing dates, set the "LC_TIME" environment variable (for example, "LC_TIME=en_GB"). If you want the ISO 8601 date format (YYYY-MM-DD), use the "en_DK" locale.

Note: there is a bug in Thunderbird where LC_ALL overrides the setting of LC_TIME. If you have old applications which require LC_ALL to be set to "C", then you might find that merely setting LC_TIME is not enough to change the date format.

In order to set this value only for Thunderbird you can either use a separate script to invoke Thunderbird that contains the following lines:

 #!/bin/sh
 export LC_TIME=en_DK  # or whatever you want
 [ "$LC_ALL" != "$LC_TIME" ] && unset LC_ALL # only necessary if set to something different from LC_TIME
 exec <FullPathToYourOriginalThunderbirdCommand>/thunderbird "$@"

make this shell script executable and place it in a directory that is in your binary search path *before* the original Thunderbird command.

OR, if you are using thunderbird 2.0, you can create a special script that thunderbird will load on startup. This can either be created as a system change by creating this file in your thunderbird/init.d directory where thunderbird is installed, OR a personal change by creating an init.d directory in your .thunderbird directory in your home directory.

mkdir -p ~/.thunderbird/init.d

Create a file named S00Locale.sh in the init.d with the contents

export LC_TIME=en_DK.UTF-8

make sure it's set executable

chmod +x S00Locale.sh

If you are on an system using the utf8 charset (like Kubuntu/Ubuntu) and get this errromessage:

(thunderbird-bin:4587): Gtk-WARNING **: Locale not supported by C library.
       Using the fallback 'C' locale.

you need to add .utf8 (or .UTF-8) to the LC_TIME export, like export LC_TIME=en_DK.utf8.

You could also see a list of all the available locales using the locale -a command:

$ locale -a
C
en_AU.utf8
en_BW.utf8

In Mac OS X, go to the "International" panel in System Preferences. The date format can be adjusted under the "Format" tab.

External links

• ConfigDate extension for Thunderbird: allows you to configure the date display format without needing to manually edit the user.js file.
• ConfigDate extension for SeaMonkey: allows you to configure the date display format without needing to manually edit the user.js file.
• International ISO-8601 Date Format on Thunderbird for the problem and fix for UTF-8 systems