There is a bug in Mozilla THunderbird, that hinders OpsEmail extension for TB. THis has been patched and reported:
We need to get the patch cleaned, so it will be included in the Moz. trunk.
Ivo van Dongen
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Working on that, see http://www.openprojectservices.org/twiki/bin/view/Developers/OpsEmailThunderbirdPatch for more details