In its recently published 2021 Chrome Extension Performance Report, website performance monitoring solutions provider DebugBear found that browser extensions can significantly slow the speed of websites. The report, which analyzes the impact that 1,000 of the most popular Chrome extensions have on browser performance and end-user experience, looks at the CPU processing time spent on different types of pages, delay to when page content renders, the CPU processing that is done in the background, and the impact on browser memory consumption. As the performance impact of extensions varies between different websites, five pages were included in this analysis: a simple test page,,, and articles on ad-heavy news websites.

Among the 100 most popular Chrome extensions, which include Loom for Chrome, Honey, and Avira Browser Safety, the report reveals that Evernote Web Clipper has the biggest negative impact on web performance, spending 368 milliseconds (approximately .37 seconds) running code on every page that users open. While this may not sound like much on the surface, if multiple extensions are installed, this can result in a major negative impact on website speed and user experience.

Another key finding in the report is how ad blockers and privacy tools can greatly improve browser performance. When testing the CPU usage of two news articles, one on The Independent and one on the Pittsburgh Post-Gazette, it was found that CPU time is 17.5 seconds without the use of ad blockers. With Trustnav (the lowest-performing blocker) enabled, CPU time decreased by 57 percent to 7.4 seconds. Also, with Ghostery (the best-performing blocker) enabled, CPU activity was reduced by 90 percent down to just 1.7 seconds on average.

“The results of this report are highly valuable to many Chrome users because they may not be aware of the impact that extensions can have on how fast websites load for them,” said Matt Zeunert, Founder of DebugBear. “Unlike most other sources of website slowness, browser extensions are actually something under users’ control. By knowing which extensions may be slowing down your browser, you’ll be able to maintain optimal performance through better management of the extensions you use.”

Extension developers can limit the performance impact of their extensions by limiting the amount of code that is run on each page and only loading code where necessary.


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