With Firefox 3.0, a new way of declaring locales is introduced, reinstating install.rdf as the main carrier file for this information. With the introduction of Firefox 2.0, chrome.manifest was introduced to contain this information, but many developers stuck to install.rdf as this file remained necessary for other information. With the new structure, install.rdf will contain <localized> tags containing all possible information on locales, like the translator's name, locale declaration and the localized description.

<em:localized>
   <Description>
    <em:locale>en-US</em:locale>
    <em:name>Extension name</em:name>
    <em:creator>Creator's name</em:creator>
    <em:developer>Developer's name</em:developer>
    <em:translator>www.BabelZilla.org</em:translator>
    <em:description>This text is only here to demonstrate FF 3.0 features.</em:description>
    <em:homepageURL>https://addons.mozilla.org/firefox/addon/addonnumber</em:homepageURL>
   </Description>
 </em:localized>

These <localized> sections cannot be handled by the WTS at this moment.

If a <localized> section is present in install.rdf when uploading an xpi, this will lead to an error and loss of information, so in order to prevent these errors developers are requested to comment out or remove any <localized> declarations in their install.rdf before uploading (but of course add or keep the locale declarations as necessary).

The next version of the WTS will be able to properly handle these sections and will also provide tools for developers to easily collect the information and re-compile a new file.

Also see the How to submit an extension? and How to update an extension? Help for instructions on how to make sure that locales are properly declared.