>There is some cost/effort to building a better browser engine. They might believe that the same cost/effort would better benefit the business if put elsewhere.
Yes, because all those years the Mozilla executive team has proved that they have a good grasp of where the cost/effort optimum lies... /s
I can't speak for how things were at Mozilla, I have no idea. But separate teams working on "rewrites" of platforms that other teams have to maintain often leads to a demoralized environment, pointless duplicated work, and elongated schedules and failure to deliver on milestones.
I've seen it several times: Often after years of promises from "the new hot" team, with them cannibalizing resources and top talent but missing milestones and still having failed to deliver, the new beast is cancelled and the value of the "old" system is suddenly recognized.
What's better? Refactor the old thing as you go. Include the "legacy" team in the development team of the new thing. Even more so, make the "new" team work on the old thing as well. Rotate developers between the two, build a culture of respect.
Not saying that is what happened at Moz, but I've seen it play out so many times. And without a concrete commitment to be forced to deliver to actual customers projects like these can just go forever noodling around in perfection-land.
Yes, because all those years the Mozilla executive team has proved that they have a good grasp of where the cost/effort optimum lies... /s