This runs at 16fps on my MBP. The title has 500 text shadows :( I've attached a somewhat reduced copy of the page.

Batch updating status flags based on WR schedule - please adjust if needed.

You can assign this to me if you like - it'll need some profiling to see (a) if the text shadows are not being cached (and if not, why not) and (b) what the exact cause of the GPU time slowness is.

Yup, as Jeff mentioned above, this is entirely due to the "interesting" text-shadow effect on the header bar. If I disable that, or scroll past it, the rest of the page is easily running at 60fps. The CSS rule for the text-shadow effect is: text-shadow: 1px 1px #2d343a, 2px 2px #2d343a, 3px 3px #2d343a, 4px 4px #2d343a, 5px 5px #2d343a, 6px 6px #2d343a, 7px 7px #2d343a, 8px 8px #2d343a, 9px 9px #2d343a, 10px 10px #2d343a, 11px 11px #2d343a, 12px 12px #2d343a, 13px 13px #2d343a, 14px 14px #2d343a, 15px 15px #2d343a, 16px 16px #2d343a, 17px 17px #2d343a, 18px 18px #2d343a, 19px 19px #2d343a, 20px 20px #2d343a, 21px 21px #2d343a, 22px 22px #2d343a, 23px 23px #2d343a, 24px 24px #2d343a, 25px 25px #2d343a, 26px 26px #2d343a, 27px 27px #2d343a, 28px 28px #2d343a, 29px 29px #2d343a, 30px 30px #2d343a, 31px 31px #2d343a, 32px 32px #2d343a, 33px 33px #2d343a, 34px 34px #2d343a, 35px 35px #2d343a, 36px 36px #2d343a, 37px 37px #2d343a, 38px 38px #2d343a, 39px 39px #2d343a, 40px 40px #2d343a, 41px 41px #2d343a, 42px 42px #2d343a, 43px 43px #2d343a, 44px 44px #2d343a, 45px 45px #2d343a, 46px 46px #2d343a, 47px 47px #2d343a, 48px 48px #2d343a, 49px 49px #2d343a, 50px 50px #2d343a, 51px 51px 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#2d343a, 484px 484px #2d343a, 485px 485px #2d343a, 486px 486px #2d343a, 487px 487px #2d343a, 488px 488px #2d343a, 489px 489px #2d343a, 490px 490px #2d343a, 491px 491px #2d343a, 492px 492px #2d343a, 493px 493px #2d343a, 494px 494px #2d343a, 495px 495px #2d343a, 496px 496px #2d343a, 497px 497px #2d343a, 498px 498px #2d343a, 499px 499px #2d343a, 500px 500px #2d343a; This gives a kind of very long, angled text extrusion effect. We have a few bugs with this kind of performance issue - that is, an individual effect which is not slow, but the effect is used dozens or hundreds of times, which adds up quickly. The best way to solve this will be to cache such stacking contexts to a surface that is pre-blended. The support for this already exists in WR - the tricky bit is coming up with the right heuristic to know when it makes sense to cache a surface like this. I'll do some experiments on this next week - I think a reasonable heuristic can be made by approximating the number of overdraw pixels with opacity / blend in an element, which is quick to calculate and is typically directly proportional to measured GPU time.

I think this is a duplicate of 1422567, but that one also uses blurs.

This is likely addressed by the picture caching work that Glenn is doing.