This firefox addon expose the currently logged-in Windows user's regional settings to JavaScript. This can be used to adapt webapp behaviour/rendering to be more user-friendly.

Example:

var rs = navigator.win_i18n.get_user_regional_settings()
if (rs) {
  console.log(rs.number_decimal_separator);
}

Currently exposed regional settings (should be self-explanatory):

• number_negative_sign
• number_positive_sign
• number_decimal_separtor
• number_thousand_separator
• number_grouping
• lang
• list_separator
• date_long_format
• date_short_format
• time_long_format
• time_short_format