Benchmark refutes Google's claim that content blockers slow down Chrome

Martin Brinkmann
Feb 17, 2019
Google Chrome, Windows 10

Google released a first draft of the new version of Google Chrome's Extension Manifest in January 2019.

The company plans to limit the webRequest API that extensions, content blockers like uBlock Origin or Adblock Plus, use currently to block certain elements on webpages. It would introduce the declarativeNetRequest API instead designed to take over.

The change, if implemented as suggested, would limit content blockers and other extension types significantly in Google Chrome.

Google explained the decision in the following way:

This begins in the browser process, involves a process hop to the extension's renderer process, where the extension then performs arbitrary (and potentially very slow) JavaScript, and returns the result back to the browser process. This can have a significant effect on every single network request, even those that are not modified, redirected, or blocked by the extension (since Chrome needs to dispatch the event to the extension to determine the result).

Basically, Google argues that extensions that use the webRequest may have a significant impact on performance. In other words, using extensions that make use of the API may slow down web browsing measurably.

content blockers performance chrome

Cliqz, a German startup that operates the Cliqz browser and owns the anti-tracking extension Ghostery, ran benchmarks recently to find out whether data would confirm Google's claim.

The company used a large dataset of popular sites and measured the performance of the content blockers uBlock Origin, Adblock Plus, Ghostery, the adblocker of the Brave browser, and DuckDuckGo's adblocker.

One of the core findings of the benchmark was that all content blockers, with the exception of DuckDuckGo's adblocker, added "sub-millisecond median decision time" to each request. In other words, the performance impact of content blockers is negligible.

The test and dataset is available publicly. The selection of content blockers can certainly be criticized, especially since Ghostery is not a full-fledged content blocker like uBlock Origin or Adblock Plus. Gorhill, the developer of uBlock Origin re-ran the test and discovered that Adblock Plus did not perform as well as outlined by the original test results.

Google mentioned content blockers explicitly but other extensions use the webRequest API as well. It is possible that some introduce high cost when using it.

While it is somewhat understandable that Google wants to address performance issues caused by extensions, punishing all for the wrongdoings of some may not be the best course of actions.

To be fair, Google is still discussing changes and noted in a comment that the company does not want extensions to break because of changes made in the new manifest version.

Now You:  What is your take on all of this?

Benchmark refutes Google's claim that content blockers slow down Chrome
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Benchmark refutes Google's claim that content blockers slow down Chrome
Google released a first draft of the new version of Google Chrome's Extension Manifest in January 2019.
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  1. Jon Bovi said on February 20, 2019 at 3:13 am

    Poor Google. Perhaps it’s time for them to release their robot army, and put an end to all the competition and naysayers.

  2. supergirl said on February 19, 2019 at 12:53 am

    the config setting appears to be “Resist Fingerprinting”….not tracking ..Sorry

  3. A Daily Reader said on February 18, 2019 at 1:35 pm

    Thank you Martin and all of you regulars from the comments section. I sincerely enjoy the articles and the discussion. While I don’t always agree with comments, it strengthens my faith in humanity to see the rational and warm exchanges. OK, not always warm, sometimes a little heated, but y’all seem like genuinely good people to me.

    I see Tom’s contribution above, as usual. But where’s Sophie today?

    Remember to donate to Martin as an advance on this year’s articles & discussions. I go to Paypal, enter [email protected], and send a couple bucks. Perhaps one of the best “subscriptions” I have. Open to other suggestions on better ways to donate.

    Thanks again to all.

  4. Jozsef said on February 18, 2019 at 11:58 am

    I don’t trust Google any more, plain and simple so nothing sinister that they come up with shocks me these days. To think that back in their beginning when it was Google Beta and a standard Boolean search actually worked, it seemed like heaven on earth. Now that search terms are more or less ignored, even when using “advanced search,” I struggle to find anything about Google to be grateful for and much to fear since they now seem predatory and amoral.

  5. supergirl said on February 18, 2019 at 4:58 am

    Its worse than that …the internet…. its Dead,Jim!…Its Dead,Jim!…Its Dead,Jim!
    {End/Star Trek Reference}

    if you have ‘Config = Anti-tracking’ enabled in Firefox/Waterfox Google’s Captchas
    set up a nearly endless loop making it REALLY Annoying to get past them.

    So if you wanna fight tracking in your browser… They will just screw you online.

    This Company needs to be labelled a ‘hostile non-combatant’ & shut down.

    In Real Life… if someone followed you all around & took notes of everything you do
    EVERYWHERE They would be considered stalkers & you could get an order of protection
    against them to make them stop.

    Why not Online?? Whats the Difference?

  6. Jojo said on February 17, 2019 at 7:28 pm

    Why does Google care? Their protestations don’t make sense!

    Even were Google correct, users who choose to use an ad blocker do soon on there own volition.

    Users who DON’T use the ad blockers will therefore enjoy better performance and those that use the ad blockers will be penalized with a slower browser response.

    If the slowdown is significant, then users won’t use ad blockers, which should make Google happy.

  7. DandelionSprout said on February 17, 2019 at 6:39 pm

    As someone who actively make lists for adblockers and other extensions, with 1 such list included in uBlock Origin; but also as someone who struggle to understand APIs in general; I think Google is in some very deep water here.

    One thing is Google trying to heavily stump Adblock Plus and uBO and the likes (Especially uBO), which is a bad enough thing already. But if it’s true what I’ve heard about declarativeNetRequest banning redirections and editable filters, I presume that it’d also break things like Tampermonkey, HTTPS Everywhere, Nano Defender, several redirection extensions, and plausibly even (Don’t take my word for the following) FrankerFaceZ and Chromium Smooth Wheel Scroller.

    Many Firefox fans were peeved when pre-WebExtensions extensions became unsupported. But it’s a whole other ballgame for most or all of the above popular Chrome extensions to break, with no easy way to update them to support the new API, could prove utterly disastrous for Chrome among the under-30 audience.

    But at the same time, Google is known to be difficult to reach out to with common sense, as I recall it took massive international (and even political) pressure to shut down their Dragonfly project mere months ago.

    Moreover, Chrome is somehow also the biggest Android browser, despite it having no support for extensions whatsoever. So those who are looking for long-fetched correlations both within Google and elsewhere, could very well end up thinking that extensions would be unnecessary to have in a popular browser.

    There’s many factors in play here, some of them may not be fully known at this point in time, so I can only hope that Google thinks about all this a bit better and realise that stumping extensions used by an 8-digit (if not 9-digit) amount of internetizens may potentially be a bad idea.

  8. Brett Cooper said on February 17, 2019 at 6:04 pm

    If google was worried about performance then it would block adsense and facebook’s tracking software.

  9. John C. said on February 17, 2019 at 4:10 pm

    Perhaps when everybody stops using Chrome… oh, that’s right. Almost every other browser is now pretty much a Chrome-clone.

    1. no name said on February 17, 2019 at 5:49 pm

      I have been using Firefox again since version 65. I’ve been using Google Chrome the last few years. Then I got annoyed at some point that you can no longer back up your profile folder and restore it to another computer. The extensions and settings like passwords get lost.
      Then I changed to Vivaldi for 2 years, because he brings some useful functions from the start, without looking fat, Chrome didn’t have them and also some extensions didn’t work reliably under Chrome. And if you ever had an extension, you always had to be careful that it didn’t do something bad for money later (e.g. injecting advertisements).
      I liked Vivaldi because Speeddial was included by default. There are only overloaded extensions in the Chrome Store.
      You could also deactivate GIF animation or play it only once.
      The Notitz function was also very practical. I also used the screenshot function very, very often. Even if I already had pages several times where the maximum 30000 pixels are not sufficient, which could be recorded vertically at most.
      I also often used the tile display.

      When I then had problems with the performance, I installed Firefox to see if they also occur there. There I noticed that the performance and the start of Firefox are better than with Vivaldi.
      So I thought to myself, give it a chance again. At least as long as the problem with Vivaldi was not fixed.

      So I installed uMatrix, uBlock Origin, Checker Plus for Gmail and 3 other extensions. I set the upper 2 bars to compact, the 2 useless placeholders right and left of the address bar removed. And still set that the download icon (to the right of the address bar) is displayed permanently, and not just when you have just downloaded something.
      Now I’ve been using Firefox for a few weeks and don’t see any reason to switch back to Vivaldi or Google Chrome.
      In the back of my mind I have also the possible castration, which concerns the Adblocker with Chrome. Let’s see how this thing ends.

  10. no name said on February 17, 2019 at 4:04 pm

    >Ghostery, ran benchmarks
    slowdown due to expansion:
    Ghostery 0,050 ms
    uBlock 0,124 ms

    Independent tester checks extensions (
    slowdown due to expansion:
    Ghostery ca. 148 ms
    uBlockca. 79 ms


  11. crambie said on February 17, 2019 at 3:47 pm

    They’re not going ahead with it (for now).

  12. Weilan said on February 17, 2019 at 3:14 pm

    If those greedy pigs remove adblockers for Chrome and even forks like Vivaldi and Opera can’t install them, then everyone will move to Firefox, despite how pathetic Firefox is.

    1. no name said on February 17, 2019 at 5:55 pm

      I have noticed that at least Firefox 65 is quite usable. On my system (Acer Swift 1) the performance is better than on Vivaldi or Google Chrome.
      I used to have Firefox stored in my head as Snailfox for years.
      This has apparently changed since the new engine and changed to web extensions.

      1. Weilan said on February 18, 2019 at 12:34 pm

        @no name

        I gave Firefox a go for about a month (December-January) and for the most part it was OK, but after about 2-3 weeks of usage, the performance started to deteriorate. My guess is that my Firefox profile got filled with junk data.

        Using the built-in cleaning in Firefox didn’t help, 3rd party stuff like SpeedyFox that were supposed to “slim” the SQL database didn’t do much, 3rd party cleaning tools like Wise Disk Cleaner didn’t help either.

        The only thing that helped was to completely delete all traces of Firefox on my computer and completely reinstall it. Only after that it worked OK, but I don’t like the idea of having to do that.

        Also Firefox struggled on some websites, like Reddit, Twitch and YouTube for example. I install Chrome and BOOM! – those websites load and perform just fine, of course Chrome is not perfect either, I can start listing its flaws too, but for the most part it handles itself a lot better than Firefox and as long as I can block ads and popups on Chrome, I will stick with it, maybe when all hell breaks loose, I will jump back to Firefox.

      2. no name said on February 19, 2019 at 1:20 am

        > YouTube page load is 5x slower in Firefox than in Chrome because YouTube’s Polymer redesign relies on the deprecated Shadow DOM v0 API only implemented in Chrome.


  13. TelV said on February 17, 2019 at 3:11 pm

    As long as Google limits these changes to their own browser I really don’t care since I don’t use it. The danger will be if they persuade Mozilla and other forks to implement the same limitations.

    The next thing they’ll do is link ads to content on youtube so that users who have an adblocker enabled won’t be able to view any videos. Wouldn’t surprise me at all if that happens since Google’s only interest is parting you from your money.

  14. noemata said on February 17, 2019 at 1:25 pm

    liars. manipulators. cliqz/ghostery/burda like google. against any immediate user experience. damn degenerated web. damn degenerated times.

  15. Paul(us) said on February 17, 2019 at 11:30 am

    More and more I am convinced that the only thing really Google is interested in is steering you in the direction of there best interest, being the companies who are paid for that purpose Google.

    1. Tom Hawack said on February 17, 2019 at 2:49 pm

      So true.

      Roger McNamee, American fund manager and venture capitalist, in other words not a leftist, in an interview to The Guardian :

      “My thought process was that this isn’t a tech story. It’s not a business story. This is an everybody story. This is a catastrophe that we’re all facing, and we don’t necessarily have a vocabulary for it, because the business model that Facebook and Google have created is something we’ve never seen before.”

      This business model is a threat to capitalism itself, to free markets and competition, democracy.

      So what can a simple fellow as myself do about it? As Rger McNamee points it out at the end :

      “So I fear that we’re now at the point where external stimuli are the only way this will happen, which is why I emphasise the role that the people who use these products need to play by withdrawing some or all of their attention and by making their voices heard with policymakers in government to force regulatory change.”

      In other words, for the least be aware. I consider avoiding as far as possible which means all of Facebook, all of Google related to an account and all of Google which may be blocked without blocking websites. All of Amazon as well, for other reasons. All of Twitter, Linkedin, all social craps.

      1. Paul(us) said on February 17, 2019 at 5:48 pm

        Tom, I am more and more convinced after studying Google their actions thru the years that Google is still watching right now through the periscope to see or they can launch without problems for themselves. Google launched up to now only tactical weapons.
        And I am more and more convinced that when Google sees even have a change Google will surface and will go nuclear ( Orson Wells scenario big brother is watching you! Version 2.0).

        Another consequence from Google going nuclear will be because now in 2019 other browsers like Firefox who are also doing the Google Goose’s pass will make it ferry difficult for a browser like Tor to create even a slightly free world.

      2. Anonymous said on February 17, 2019 at 7:01 pm

        “Orson Wells scenario big brother is watching you!”

        You mean George Orwell (in his “1984” dystopian science-fiction novel). Interestingly this British author wrote this book in 1949 as a caricatural anti-sovietic pamphlet, while in the real world it’s finally surveillance capitalism that achieved the level of technological surveillance imagined in the book, like the telescreens :

        In fact technological surveillance is today *far more* extensive than described in the 1984 dystopia.

      3. Paul(us) said on February 17, 2019 at 8:50 pm

        Anonymous, I meant Orson Wells “The war of the worlds”

        Where Google is the world and the user the bad character which threatens the earth.

        George Orwell is another coop of tea! the 1984 anti-utopia society George Orwell outlines where already have had even before 1949.
        The final stone in that process was in 1954

  16. Mr. Stank said on February 17, 2019 at 11:13 am

    I wonder what is the performance of using all of them at the same time.

  17. AnorKnee Merce said on February 17, 2019 at 10:53 am

    I would think that most desktop Chrome users do not mind the browser being a bit slower if they can block Google’s intrusive ads, tracking or collection of user-data.

    Seems Google is trying to limit user-choice, in order to further her business interest or profit-making.
    ……. Fyi, Chrome for Android does not allow extensions = tons of intrusive ads from Google. Firefox for Android allows extensions, eg Adblock Plus, No Coin, etc.

    If not careful, Google’s desktop Chrome will lose market share with this anti-user move = self-destruction by super-greed.
    P S – In non-English-speaking China, very few Android users use Google Play Store or Chrome.

  18. Anonymous said on February 17, 2019 at 10:47 am

    Cliqz is a spyware company well known for this privacy scandal where they collaborated with Mozilla to steal users sensitive data :

    The privacy policy of their “anti-tracking” Ghostery extension
    allows collection of sensitive user data by default. Unsurprisingly this extension is anyway “featured” by Mozilla, that owns part of Cliqz.

    Their study
    is published on their “” site, ironically dedicated to criticizing tracking. Even more ironically, they sell themselves as a “privacy company” and claim there that “We believe in an internet where the user’s interest really does come first.” :

    All this including this study is PR manipulation from one of the worst spyware offenders trying to buy themselves a new privacy virginity. Competing with their parent company, Mozilla corporation, on who’s the worst hypocrite.

    1. Yuliya said on February 17, 2019 at 5:35 pm

      This. I would never trust cliqz or mozilla. Both are collecting and selling users data, while lying to threir users. Fuck them. They are equally evil to Google or Microsoft nowadays. The world would be a better place without them.

      1. Ken Saunders said on February 18, 2019 at 12:13 am

        mozilla…selling users data….equally evil to Google

        Okay, sure, and please provide proof.

        What browser do you use?

      2. Tamris said on February 17, 2019 at 9:53 pm

        Since even Mozilla apparently can’t be trusted, what browser am I supposed to use? Tor Browser? Seems like the only option since I’d rather die than use a blink based browser.

      3. noemata said on February 18, 2019 at 10:07 am


        brave is based on chromium, but ungoogled:

        and prepared:

        & has an integrated tor – browser.

        to hell with mozilla & co. . on linux too.

  19. pat said on February 17, 2019 at 10:26 am

    It’s stupid, all informed users nowadays know that an adblocker is mainly used to speed up the loading of pages since the Internet has become a real garbage can of ads, scripts, useless elements, third party sites of no useful uses…..
    The last time I had fun surfing the net without a uBO, my God, I almost cried. ;-)
    It looked like there were more lines in the elements blocked by uBO than on the web page.

  20. Roebie said on February 17, 2019 at 10:24 am

    Once again, Google tries to rule the world anyway it sees fit. It’s about time this company gets stopped in its dictatorial path of conduct.

    1. Anonymous said on February 18, 2019 at 3:16 am

      Eric Schmidt and Jeff Bezos are both CIA agents. Along with Bill Gates (another agent?) they control 90% of the internet via their global network of datacenters and software AKA “the cloud”. Try to find one thing in the world that isn’t within the reach of Google, Microsoft & Amazon, their control extends to the real world through cell phones, smart speakers (literally surveillance devices), cameras, IoT devices, game consoles, and social media.

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