Surprise (not): Extensions may impact a browser's performance

Martin Brinkmann
Feb 13, 2019
Google Chrome

Most web browsers nowadays support extensions that add, change, or remove certain functionality from the browser itself or websites.

Extensions may be installed to block advertisement or tracking, add functionality to websites, keep track of item prices, change the New Tab Page of the browser, or correct your spelling.

It should not come as a surprise that extensions that do get loaded consume some resources. 26 different Chrome extensions were analyzed recently to find out if they impact the browsing performance.

Popular extensions such as uBlock (Origin I suppose), Adblock Plus, HTTPS Everywhere, Grammarly, LastPass, or Google Dictionary were selected for the test.

The results confirm what many Internet users who use extensions probably know already:

  • The average extension does not impact performance significantly.
  • The more extensions you use, the higher the performance impact.
  • Privacy tools improve performance on pages with lots of advertisement or tracking scripts even though they have a small initial cost.
  • Some extensions, especially those with page-related actions, impact performance more.

Some extensions consume more CPU than others. Honey, a shopping extension, added 636ms of extra CPU time when installed. Grammarly, a spelling and grammar checker, more than 300ms, and Evernote Clipper and StayFocused, more than 200ms each.

Of all the tested content blockers, Ublock (again, I assume uBlock Origin is meant) used the least amount of CPU when loading tested sites. AdGuard, AdBlock, and AdBlock Plus all used more CPU in the conducted tests.

One privacy-focused extension, Privacy Badger, used less CPU than uBlock whereas Ghostery used more.

Extensions that don't use best practices, e.g. an extension that is designed for a specific website but designed in a way so that it runs on all sites, impact performance more than they should. Chrome extension developers should also avoid running content scripts on document_start, and aim to keep the JavaScript that is included as small as possible.

It would be easy enough for the developer, usually, to address some or even all of these issues.

Closing Words

Researchers would have to repeat the test in a controlled environment and larger sample size to confirm the findings.

While Chrome has been at the center of the analysis, it is likely that the findings will hold true for other browsers as well.

The researcher did not look at memory usage or power consumption to find out if extensions impact those metrics as well.

A good advise is probably that you should try and run a minimal number of extensions in your browser of choice. Apart from improving performance, you may also improve privacy.

Now You: How many extensions do you run currently?

Surprise (not): Extensions may impact a browser's performance
Article Name
Surprise (not): Extensions may impact a browser's performance
Installed browser extensions may impact the web browser's performance in regards to CPU usage and the loading of websites.
Ghacks Technology News

Previous Post: «
Next Post: «


  1. TelV said on February 15, 2019 at 2:06 pm

    I have 23 add-ons installed on Waterfox.

    – Adblock Plus 2.9.1 (don’t like menus in subsequent versions)
    – Add To Search Bar
    – Behind The Overlay
    – Canvas Blocker (version 0.4.4b)
    – Class Theme Restorer
    – Close Tab By Double Click
    – Context Search
    – Decentraleyes
    – Element Hiding Help for APB
    – Google Redirect ReWrite Remover
    – Google Search Link Fix
    – HTTPS Everywhere
    – I Don’t Care About Cookies
    – Image Max URL
    – Legibility (to turn pale grey fonts to black)
    – No Resource URI Link
    – Privacy Badger
    – ReminderFox
    – Self-Destructing Cookies
    – Status-4-Ever
    – Thumbnail Zoom Plus
    – User Agent Overrider (only enabled when posting to Github)
    – Video Download Helper (disabled most of the time)

    I consider all of them to be essential. :)

    1. Steve said on February 16, 2019 at 12:44 am

      Essential to reduce performance?

      MMVC (my mileage varies considerably) from you list I have HTTPS Everywhere. I did trial a couple of the other but found alternatives. For me, uMatrix controls a lot. Click & Clean takes care of cleaning up.

      Overlays are incredibly annoying. I just installed behind the overlay – thank you.

  2. DragoCubed said on February 15, 2019 at 12:49 am

    Here are the extensions I use:

    Mute tab
    uBlock Origin
    uBO Extra
    Nano Defender
    View Image

    I find browsing to be so much faster with my extensions. I wouldn’t need 4 of those if Google didn’t remove so much and blocked something for privacy and security:
    Mute tab, MuteTab, uBO Extra and View Image. I have a similar setup on Firefox except with Firefox on my phone I have Google Search Fixer and Video Background Play Fix. Those two wouldn’t be necessary if Google weren’t so annoying.

    Speaking of which, Google’s explanation for why limiting what extensions can do with Manifest v3 is BS. You can see my reasons why on Disqus:

  3. Dave said on February 14, 2019 at 4:36 pm

    I have 8 add ons for FF and all of them are security and privacy related.

    To me autoplay videos are a security threat as it’s unknown and unexpected data being downloaded to my PC without my consent.

    My PC is so fast I can’t tell a difference in page loading time.

    I use only 3 on Edge as I’m not concered with privacy there, quite the opposite, I want to leave a clear and obvious trail so it will be obvious if someone accesses one of my accounts from a different “trail”.

    One add ons does slow it down. I use F.B.Purity and it definitely slows down the loading of my FB page (I use only for family) but it’s well worth it as it blocks everything I ask it to. Just a quick guess, that’s about 75% of the site.

    Now on mobile, Adblock plus makes a huge difference on FF. The loading bar always stalls at about 10% for a few seconds but it’s still worth it. It’s not to save data as we have so much rolled over it’s insane, it’s about being able to see what I want to on the tiny screen.

  4. basicuser said on February 14, 2019 at 3:08 pm

    @ Nico.
    Thanks for your input. This is a W7 Pro machine with 2 G of memory. I realize there is a lot of duplication between the filters, but I see a longer page load time while in PM Safe Mode with no filters compared to using the filters. Anyway, browser performance and memory usage are way down my list of priorities, with security, anti-tracking and bandwidth usage taking precedence. I’m on a slow satellite ISP with a 5 Gig monthly allowance. BTW, surfing with JavaScript disabled has the greatest effect on limiting bandwidth usage and speeding up page loading. YMMV.

    1. Nico said on February 14, 2019 at 7:21 pm

      You can use the same filters you have in Adblock Latitude also in uBlock Origin and they will have the very same effect there.
      Plus uBlock Origin has some very powerful filters of its own (that do not work in Adblock Latitude).

      And since bandwidth is your bottleneck, now you have to download the same filterlists twice, each time they need to be updated…

  5. Anonymous said on February 14, 2019 at 4:37 am

    These “researchers” are parasites.

    1. John Fenderson said on February 14, 2019 at 5:45 pm

      Why do you say that?

      1. Anonymous said on February 14, 2019 at 8:49 pm

        Because they are at the ‘Origin’ of what ‘I suppose’.

      2. John Fenderson said on February 14, 2019 at 9:52 pm

        I genuinely have no idea what point you’re making.

  6. Franck said on February 14, 2019 at 4:32 am

    Thank you very much for this great reminder !

  7. TigerMann said on February 14, 2019 at 1:10 am

    I have two profiles set in Firefox Quantum. One has 12 extensions, the other has the same 12 but an additional 16 of which I use but obviously not on every occasion but the extensions are all ones that I need at various times. If I open 25 tabs in profile one and the same in profile 2, I can surf for hours with no problems yet in profile 2, my system slows to a stop after about 10/15 minutes to the point that I have to shut down the browser which takes a couple of minutes due to 8GB of RAM fighting to get back into use. If someone has a solution to how you can have as many extensions as possible and open as many tabs without any issues, I will probably marry them!!

  8. Redblast said on February 14, 2019 at 12:04 am

    I’m using 22 extensions on Firefox.

  9. basicuser said on February 13, 2019 at 11:59 pm

    My primary extensions in Pale Moon are uBlockO, AdBlock Latitude and surf with JavaScript disabled using Toggle JavaScript. I also use SpywareBlaster, SpyBot Anti-Beacon portable to stop some of Microsoft’s slurping, and HostsMan to add sites not usually included in the above filters like Facebook, Twitter and Disqus. Over all, they reduce bandwidth usage and give some protection from trackers and ad ware/malware.

    1. Nico said on February 14, 2019 at 11:58 am

      You should not use 2 ad blockers (uBlock Origin and AdBlock Latitude) together. That causes conflicts and of course more memory usage.
      I suggest you to use only uBlock Origin (far superior).

  10. Steve said on February 13, 2019 at 11:40 pm

    I haven’t been using it long but am starting to like uMatrix. Quote:

    “Point & click to forbid/allow any class of requests made by your browser. Use it to block scripts, iframes, ads, facebook, etc”.

    If you decide to try it, make sure you read the full overview of the extension to work out where to get help.

    It is not entirely intuitive to use but broadly, click the icon then use the Matrix to allow/disallow. Click the top part of the cell containing a number to allow; the bottom half to disallow. After that, refresh.

    You can create ‘My rules’. That lesson is still to be undertaken.

    HINT: The logger is handy to help you determine precisely what is is that is ‘breaking’ a web page (e.g. ssl.gstatic was blocking my Google+ logon).

    Congratulations. ghacks comes up with nothing blocked and nothing to block.

  11. John Fenderson said on February 13, 2019 at 6:33 pm

    “How many extensions do you run currently?”

    I run four (on Waterfox)– DownloadThemAll, NoScript, Classic Theme Restorer, and an extension that prevents websites from taking control of the right click action.

  12. jccalhoun said on February 13, 2019 at 6:27 pm

    Honey used to kill Firefox for me. I got in the habit of keeping it disabled unless I was on Amazon.

  13. VioletMoon said on February 13, 2019 at 5:51 pm

    Curiosity–about:performance in Firefox reveals the performance impact for memory for each extension. I think Martin mentioned it once. AdGuard is by far the most resource hungry using 46.1 MB of RAM. Other high usage extensions = HTTPS Everywhere and UBlock Origin.

    Do the results really mean anything other than RAM usage and maybe browser slowdown?

    1. ULBoom said on February 13, 2019 at 11:09 pm

      The amount of memory used may or may not be related to speed. I use AdGuard too and it’s currently consuming 24 Mb. If I disable it, the 24 Mb returns but page loading is dreadful. Otherwise, the FF Task Manager itself (about:performance) often uses more memory than the other add ons that load on start (decentralize, flash video downloader, e-cleaner.) The other 4 add ons don’t load until used.

      Re: AdGuard, I’ve had good results with base, spyware and social media filters on, all other buttons beside number of blocked ads indicator off. FF does phishing and malware filtering, so does my AV and I keep the hosts file bad sites filters updated. AdGuard’s annoyances filter has had quite a few versions that slowed browsing, kept videos from playing and interfered with element blocking. It doesn’t seem to improve browsing much.

      If you overdo AdGuard, it can definitely bog down browsing with little or no improvement in privacy or security.

    2. gorhill said on February 13, 2019 at 9:46 pm

      > about:performance in Firefox […] Other high usage extensions = HTTPS Everywhere and UBlock Origin.

      uBO with default settings/lists is typically under 8 MB with normal operating mode. Of course the figure will increase when using the logger and/or auxiliary pages (which is true for all extensions), but once those auxiliary tools are closed away, uBO should return to its baseline memory usage.

  14. Tamris said on February 13, 2019 at 2:00 pm

    I only use 3 extensions currently. And yes, extensions do impact browser’s performance, with uBO disabled, my old laptop chokes on 99% of websites while when it’s enabled, everything’s smooth af.

  15. MartinFan said on February 13, 2019 at 1:59 pm


    Disable HTML5 Autoplay since we are on a 10 Gb a month data plan from satellite internet provider.

    UBlock Origin & Privacy Badger.

    1. Robert Ab said on February 14, 2019 at 7:42 am

      Disable HTML5 Autoplay does not work well. Use AutoplayStopper instead.

  16. chesscanoe said on February 13, 2019 at 1:07 pm

    In spite of always believing the fewer browser extensions the better, I find i am now using 11 extensions in Chrome, but still none in incognito mode. Performance impact is unmeasured but not a significant impact. Potential privacy threats are more important to be concerned about IMHO.

  17. Weilan said on February 13, 2019 at 12:51 pm

    I think uBlock Origin is the best when paired with Poper Blocker. I don’t understand who would use something else, especially Adblock Plus, which at one time was great, but then it sold out.

    1. Anonymous said on February 13, 2019 at 8:14 pm
    2. Tom Hawack said on February 13, 2019 at 6:49 pm

      ‘uBlock Origin’ makes popup blockers irrelevant. uBO itself includes a popup blocker (bottom-right : ‘Click to block all popups on this site’) which I never need by the way : good filters do the job.

      1. Shiva said on February 13, 2019 at 9:51 pm

        Simply I prefer a global blocking with withelist. Moreover on if you click on “Choose Image’ you can see the difference with ublock and Popup Blocker Ultimate. Ok, this isn’t the right example…, but it can explain the strict mode. Also I use Waterfox as main browser and I like Popup Blocker Ultimate options unlike webextension.

    3. Shiva said on February 13, 2019 at 4:31 pm

      uBlock Origin, Popup Blocker Ultimate (Strict Pop-up Blocker good as well), HOSTS file updated with HostsMan.

      “When you install or use the Poper Blocker Product, we collect from you: the type of device, operating system and browsers you are using; the date and time stamp; browsing usage, including visited URLs, clickstream data or web address accessed; TabID; the browser identifier; and your Internet Protocol address (trimmed and hashed so that it cannot be used to identify you). We may disclose or share this information with third parties as specified below and solely if applicable.”

      1. Topical said on February 14, 2020 at 12:13 am

        Is it in Windows 10? Does it not slow things down at startup for you? Last time I added hosts to my domain I saw the dns cache process was causing high disk usage after startup and internet didn’t work till it was loaded. Any suggestions?

  18. user17843 said on February 13, 2019 at 12:38 pm

    When it comes to blocking, best performance will be reached with network-wide DNS filters like Adguard DNS, Adguard Home or Pihole and only blocking annoyances and privacy related scripts with uBlock Origin in the browser.

    Which brings the necessary browser filters down to around 24,000 network and 43,000 cosmetic filters (Easyprivacy, Fanboys Annoyances)

    Adding other blocking extensions will only lead to a performance reduction.

    Other types of extensions will probably be easier on performance if they are only activated after a click on the extension, which can be configured in the settings.

    1. zakius said on February 13, 2019 at 5:12 pm

      hosts level blocking of all-junk domains (no need to resolve names remotely = saved time) + blocking of third party domains by default + carefully crafted list of resources to block + some cosmetic filtering would be the most efficient I assume

      1. user17843 said on February 13, 2019 at 6:38 pm

        @zakius: Forgot to mention I implied the easiest out-of-the-box solution.

    2. Reader said on February 13, 2019 at 5:01 pm

      May of us prefer faster DNS like with pfSense + pfBlockerNG. I get your point but Adguard DNS is definitely ‘not for everyone’.

    3. Tom Hawack said on February 13, 2019 at 3:59 pm

      I’m running uBlock Origin with presently 156,842 network filters + 97,383 cosmetic filters, no noticeable page rendering impact.

      I have +- 45 extensions of which I could consider uninstalling 5 or 6 perhaps even if I’m aware that one only hungry extension may eat more than several others less hungry.

      I don’t focus excessively on speed when it comes to tenths of a second. Up to now the only true causes of sites displaying slowly has never been but these sites themselves, poorly crafted.

      There’s an interesting site dedicated to testing pages,
      GTMetrix at

      Ghacks (“our” beloved Ghacks!) gets an A, the site displays as fast as an uppercut.
      A counter-example is which is verrry sloooow to display, and GTMetrix explains why.

      So what I mean is that, if Webextensions, their number but also their specific hungerness counts of course, it is mainly the quality of a Website that determines its velocity. IMO need to say? Needed or not; said!

Leave a Reply

Check the box to consent to your data being stored in line with the guidelines set out in our privacy policy

We love comments and welcome thoughtful and civilized discussion. Rudeness and personal attacks will not be tolerated. Please stay on-topic.
Please note that your comment may not appear immediately after you post it.