O'Reilly Boston Training CenterIn Person and Online Training CoursesCheck it out today!
OSCON, London, UK • October 17-20 • Save 30% PC30DWALSH

View Browser Repaints in Google Chrome and Mozilla Firefox

By  on  

One goal of super-optimized websites is to prevent browser repaints due to changes in a block's style or content. There are numerous ways we intentionally (or unintentionally) trigger block repaints, but the browser does it so quickly we have trouble seeing when and where it happens. Recognizing the importance of allowing developers to micro-optimize their pages, the Chrome and Firefox teams have added features to their browsers to allow us to see those repaints. Here's how to do it!

Google Chrome & Canary

The repaint feature needs to be enabled at startup for Chrome and Canary with the --show-paint-rects config:

open ./Google\ Chrome\ Canary.app --args --show-paint-rects

Be sure to include --args in your command or you'll run into problems opening the browser. Repaints will display on each site you visit.

Mozilla Firefox, Aurora, Nightly

To view repaints in Firefox and Aurora browsers, you need to enable an about:config option. The option name is nglayout.debug.paint_flashing. Turn this option to true and you'll quickly see repaints as the happen!

At the time of publish, only nightly exposed this config feature.

I recommend you take a few moments to scope out the repaint frequency on your websites and see what you can do to improve performance!

Recent Features

  • By
    From Webcam to Animated GIF: the Secret Behind chat.meatspac.es!

    My team mate Edna Piranha is not only an awesome hacker; she's also a fantastic philosopher! Communication and online interactions is a subject that has kept her mind busy for a long time, and it has also resulted in a bunch of interesting experimental projects...

  • By
    I’m an Impostor

    This is the hardest thing I've ever had to write, much less admit to myself.  I've written resignation letters from jobs I've loved, I've ended relationships, I've failed at a host of tasks, and let myself down in my life.  All of those feelings were very...

Incredible Demos

  • By
    Facebook Open Graph META Tags

    It's no secret that Facebook has become a major traffic driver for all types of websites.  Nowadays even large corporations steer consumers toward their Facebook pages instead of the corporate websites directly.  And of course there are Facebook "Like" and "Recommend" widgets on every website.  One...

  • By
    Xbox Live Gamer API

    My sharpshooter status aside, I've always been surprised upset that Microsoft has never provided an API for the vast amount of information about users, the games they play, and statistics within the games. Namely, I'd like to publicly shame every n00b I've baptized with my...

Discussion

  1. Joe Zim

    It doesn’t look like the videos are working (in Rockmelt or Firefox)

  2. x

    Can’t see anything on Opera.

  3. Clentdc

    so what am i supposed to do with this ?
    “open ./Google\ Chrome\ Canary.app –args –show-paint-rects”

    paste it in the command line or what? im in chrome://flags, in Canary and now what?

  4. iwin

    Can’t see anything on Firefox, view repaints in Firefox and Aurora browsers

  5. dumex

    Can’t see anything Chrome.you need to enable an about

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!