Probably an unpopular opinion: Never. Mozilla is a hollowed out shell, destroyed by monetary needs. Clearly, today's Firefox, let alone Mozilla, is no longer a bastion of the free web, but an example of how late stage capitalism can destroy such wonderful projects.
They spend money on social causes, advocacy, and not purely on engineering. It has a product in a niche the overwhelming majority of people don’t want to pay for.
As free-to-play games have demonstrated, you don't need an overwhelming majority of people to pay. There are even ways to find out if it is going to work, such as say a crowd source campaign to pay for n years of browser maintenance and development with various levels of branded merchandise so people can signal their allegiance at conferences. So far I've just seen a donation link for the foundation, which gets a lot of hate because it funds all the stuff lots of potential donors want Mozilla to stop doing.
When will Mozilla stop making boneheaded decisions like this?