MesQuilla

FiltaQuilla's "Print" filter action simply calls a standard standard "Print" operation inside of Thunderbird. I don't really know how to translate your "open the email" into the internal order of events that need to happen to get Enigmail to fire and do its thing. So in short, no I don't have any ideas.

Unfortunately you are working at the edge of two extensions. The "action" part of FiltaQuilla's Print action is only nine lines of code, so it would not be difficult for Enigmail's author to look that over and suggest what could be changed to better integrate here, which could then either be incorporated by one of the extensions, or by you in a custom modification of FiltaQuilla.

In the future, I hope to incorporate a Javascript filter action into FiltaQuilla similar to the existing JavaScript search term, which would then allow advanced users to experiment themselves on modifications to the filter actions for unusual requirements.