I know their strategy is "everything online", but if 20+ million people are using it (from the article) then that market doesn't look like such a waste of time, does it?
I suspect that unlike Firefox, which actually brings in money (mostly from search engine referrals, specifically from Google), Thunderbird doesn't bring in any significant money, if at all.
Mozilla is a non-profit (or is it a not-for-profit?), but I guess they're trying to make each project self-sustaining, and if thunderbird doesn't provide any bacon (pure speculation on my part here), then -- yes, that market might look like a waste of time.
For anyone working on software at the scale Mozilla is, this truth will be recognizable: focus can be a lot more important than financing.
Mozilla has and will continue to invest heavily in projects which have no or minimal revenue associated with them. Sustainability matters, of course, but there is no rule that every project or product must be individually sustainable.
