Beware: the solution that will be presented will NOT provide any decent level of anonymity. Thunderbird could leak lot of personal information in other ways than just your IP address. Please use Tails if you need something serious about anonymity

I have some account that I would like to pass through tor. More specifically, I’d like to use hidden services to get  more bandwidth, no exit nodes, and don’t bother the server operators with the care of hiding my IP at all. I also have some “plain” account with my public-identity. All in the same thunderbird instance. I’d like to have the first account through tor, while the other on the clearnet.

The solution is just the usage of FoxyProxy standard, configuring a  proxy for tor (socks host 127.0.0.1 port 9050) and adding *.onion* to whitelist.

After that, you can just use hidden services on your account configuration where appropriate, and everything will work.