While completely understanding that an email client is orders of magnitude less than a browser resource wise and is not going head to head with a chrome monster, could you get 150M from a group of not google customers, move it into MZLA and operate firefox at 100x the cost of Thunderbird?

The entire Thunderbird project moved from being a part of Mozilla Foundation, which it was a part of since 2017, to the newly founded MZLA Technologies Corporation.

On the spending side, expenses amounted to $1.55 million US Dollars in 2020. Most of the money was spent on personnel, more than 82% …

The Thunderbird team consists of 15 people currently, the majority are engineers …

https://www.ghacks.net/2021/03/22/thunderbird-financial-report-2020-shows-strong-year-to-year-growth/