re :My Win7 default is set to short: dd-MMM-yy.

Settings > Control Panel > Regional and Language options > Formats tab

• http://www.sevenforums.com/tutorials/3527-format-regional-language-change.html

Make sure the format is for eg: English(UK) Is dd-MMM-yy a typo ?

Check Short Date is: dd/MM/yy

Tks for your answer. I have attached a screen shot now. My Win7 default is indeed set to short: dd-MMM-yy. While Thunderbird displays dd-yyyy-mm.

I cannot find "dateformat" in my config editor, contrary to http://kb.mozillazine.org/Date_display_format. My incoming mail is displayed as dd-MMM-yy hh:mm

Sorry for delay. I've discovered that there was an old bug: https://bugzilla.mozilla.org/show_bug.cgi?id=253883

It would seem that the MMM is causing the problem. You could create a new bug offering info such as OS, version of TB, settings, where format works ok and where it does not. It may also be worth putting in the link to the old bug as well.

It seems that changing the short date in "Region and Language" corrupts the "search messages" date format for English US, but not for German

Locale | Region and Language short date | TB email | TB search messages English US | default: M/d/yyyy | M/d/yyyy | M/d/yyyy English US | dd-MMM-yy | dd-MMM-yy | dd-yyyy-M <- WRONG German | default: dd.MM.yyyy | dd.MM.yyyy | dd.MM.yyyy German | yyyy-MM-dd | yyyy-MM-dd | yyyy-MM-dd

I have updated bug https://bugzilla.mozilla.org/show_bug.cgi?id=637133 accordingly.