Changes

To deploy a extension with thunderbird for the first time (the user does not already have an profile) or if you have an updated version of thunderbird simply place the extensions in the in the application's distribution directory %PROGRAMFILES%\Mozilla Thunderbird\distribution\extensions ([https://developer.mozilla.org/En/Developer_Guide/Customizing_Firefox#Including_extensions_with_your_distribution_of_Firefox source]). The extension will be activated after the first start of TB.

Note : (testing with thunderbird 10) the filename apparently must be <tt>{extension-id}.xpi</tt> (to be found within the unzipped .xpi in install.rdf), not the usual filename it downloads as from addons. Note2: during an installation, thunderbird deletes all files in dir \distibution and put his own extensions there (i.e. tbtestpilot@labs.mozilla.com.xpi), so copy your files after the installation of TB (use a lower priority).