As promised, I’m going to call out Firefox Layout & Rendering code changes that my team has been working on. This bug fix from Bas Schouten (as reviewed by Robert O’Callahan) was one of those light-bulb code changes that have really advanced my understanding of the Gecko Layout Engine’s graphics code:
This check-in implements “Paint Flashing”, a diagnostic tool that shows when the browser is invalidating (or repainting) a screen region that has changed. It’s very useful for diagnosing redundant (painting too often) or greedy (painting too large an area) invalidation. Both kinds of bugs are notoriously hard to find.
Paint Flashing will paint a random color (at 20% opacity) to indicate the “damaged” area of the screen that the browser is repainting. You can enable Paint Flashing by setting this preference to true: