Look at issues, engage with the developers and do smaller commits into Chromeium or Firefox and then apply for a job at Mozilla, Google, or Apple once you have

Look at issues, engage with the developers and do smaller commits into Chromeium or Firefox and then apply for a job at Mozilla, Google, or Apple once you have a bit of a portfolio with the project. Firefox has the benefit of hiring remote so you don't need to be near a campus of one of the other big companies. I work in Open Source and there are plenty of companies that build their business around a product and hire at market rates, normally they have a SaaS model of operation, but you'll have to set your sights a little lower than Chrome or Firefox. These companies include Ghost, Mongo, Elastic, Basho, Cockroach Labs, Automattic (Wordpress), Silverstripe, and countless more. Another way to do it is to do postgraduate work at a university and get a grant, I know people who work on the Rust compiler in this capacity.