At the same time, you want a browser that keep working with the web at least on the same level as Firefox is right now.

Servo is getting us 80% there, the remaining 20% of quirks, non-standardized behavior and web sites coded with only Chrome/Fx/IE in mind are going to be increasingly difficult to cover.

On the other hand some pieces of servo are close to have "full" compatibility. That means that we can put them in Firefox already.

The result is that web coverage alignment between Servo and Firefox increases which is great for Servo, and the performance and safety between them improves as well which will benefit Firefox.