I don't know that they would need to sell Thunderbird as a whole bundled product/service like Hey; they could launch a paid email service (in the "it's not Gmail" market occupied by Proton, FastMail, Posteo, etc.) and use that money for work on Thunderbird.
Not so different from having a VPN service and using it to bring in money for Firefox.
I was at Mozilla for a few years. I'm quite sure there was ideological tension with some around accepting Google's money, but I think the bigger issue was not having a diversification of funding and feeling like that one pillar could bring things down. In theory the changes in the mid-2010s to multiple international search providers should have helped with that, but the American pillar was Yahoo. I don't think that did Mozilla a lot of good after the Verizon buyout.
(All said, seems every time I comment something Mozilla, ex-upper management makes it clear in thread that the view from the ranks or my five-years-gone memory is incomplete, so take with as much salt as you need.)
Thing is, Mozilla's been talking service focus and funding diversification for awhile now. I'm not sure what they expect to change to make it more successful this time. Cutting payroll is an extension, not a solution.
> Furthermore, Mozilla's contract with Google to include Google as the default search provider inside Firefox is set to expire later this year, and the contract has not been renewed. The Google deal has historically accounted for around 90% of all of Mozilla's revenue, and without it experts see a dim future for Mozilla past 2021.
If that's the case, I doubt they have another option.
For the Mozilla Management, not the Company itself.
Yes, but not enough to pay the management staff (whatever they do)