No, the funds are Thunderbird's alone, originating from donations. Mozilla Foundation is just their fiscal home. Thunderbird Council went shopping for a new fiscal home for a while, even considering The Document Foundation, but decided to stay with MoFo: https://blog.mozilla.org/thunderbird/2017/05/thunderbirds-fu...
> Isn't it Upwork are hiring a programmer to work a contract for Thunderbird?
The Mozilla Foundation just forces Thunderbird to use Upwork as the channel to hire people. I think it's obvious that if Thunderbird Council was able to decide, they would never use Upwork.
Incidentally there was a post that was heavily critical of Upwork but is now "dead", it included points like:
>Then they take a 2.75% cut from the client, a 20% cut from the freelancer //
It seemed, factual, apposite, and informed; definitely strange it was killed.