Following up on another question about open source funding, how does it usually work when there is funding to pay for the dev's work, then someone new joins in and makes significant contributions? Does the original dev still keep everything? Do you split the funds between the devs? If so, how do you decide how much each person gets? Are there examples of projects where something like this has happened?
Well, when someone joins to make contributions, there isn't some requirement to pay them for their "work." That's kind of the entire point of Open Source. Everyone is working on a volunteer basis to contribute.
Now, OSS projects that have money backing them often have different ways of "distributing" the money based on how large their organization is.
How Mozilla distributes the money it gets from Google to Firefox developers probably isn't the same as how an independent developer, working on a project alone, would "distribute" their "income." In the case of the indie developer, it's probably a Patreon that goes into their "coffee money" account. They are under no requirements to "share" that with anyone else who contributes to development.
Just like if I contribute to the Firefox codebase, Mozilla isn't required to "share" some of that sweet Google money with me.
The people who end up getting money for their contributions via corporate "donations" to keep them working on OSS is different than people who just get random donations. Both amount to the same thing though, the donations are to keep them working on the OSS project instead of needing to get a day job. Generally this means you need to be high enough skill level that your skills are actually, actively in demand in the workplace, and that paying you to keep working independently on OSS is providing value to the private company.