I'm not sure which part it is in their accounts, but their Form 990 says:

https://stateof.mozilla.org/pdf/Mozilla%20Foundation_Form_99...

> MZLA TECHNOLOGIES CORPORATION share of total income: $10,760,074

So they don't break it down, but around 10 million went to the corporation that runs Thunderbird and other projects (versus 658 million to the one that runs the browser)