You can't for a number of reasons. As other people have said this catastrophically underestimates the complexity of maintaining a code base for a browser.

they’re often 3–5 years behind other browsers in implementing new web standards

I don't even think that's remotely true. My understanding is that it's on the order of a few months to a year, and it relates to things that are negligible to the average end user. They are edge case things like experimental 3d rendering. The most significant one I can think of is Webp, but they resisted adoption for principled reasons relating to Google's control over that format and aggressive pushing of it, which is a good thing not a bad thing, and an important example of how rushing to adopt new standards it's not necessarily just a sign of browser health but also an anti-competitive practice intentionally pushed by companies that have money to throw around for that purpose.