AdBlock/Adblock plus make YouTube consume a lot more CPU

Watching YouTube with AdBlock results in a 17% increase in CPU usage. The issue even affects YouTube Premium users, whose ad-free subscription normally doesn't display ads. However, their CPU usage still increases on average by 15-17%.


Many users on Reddit noticed a higher processor load and a simultaneous decrease in site operational speed, but they did not initially realize that this was connected to YouTube and AdBlock. Even though YouTube has been caught modifying the code to slow down video loading, this time it is a different story.

The recently released AdBlock versions 5.17 / AdBlock Plus 3.22 are the cause of the issue. The author of uBlock Origin, Raymond Hill, carried out a deep investigation of the aforementioned additions and concluded that they really are two to blame. Here are the key takes from his investigation.

The AdBlock extension slows down YouTube

The problem arises from multiple code paths and impacts various websites when the problematic code paths are activated. Specifically on YouTube, the issue lies within the injected content scripts, but performance problems in the background script can affect other websites, particularly those with dynamic webpage updates.

This performance regression affects users who made the unfortunate choice of using both Adblock Plus and AdBlock together more severely.

The Firefox Profiler in a profile with Adblock Plus 3.22 reveals that out of 41 seconds, over 19 seconds were spent in ABP's content script code injected into the YouTube webpage.

Adblock Slows Down Youtube

According to Hill, only disabling ABP or AdBlock is not sufficient to make the performance issues go away: When disabling an extension, its content scripts are still present in webpages.

You need to force a reload of those webpages. Best is to reopen webpages in new tabs.

In November 2023, Reddit users noticed that YouTube was loading slower in browsers with ad blockers. Initially, Firefox users experienced this issue, with YouTube videos taking several seconds longer to load compared to Chrome. Later, users of Edge, Brave, and Chrome also started reporting similar problems. The cause was determined to be code added to the JavaScript file that slowed down the loading time of the page by five seconds.

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Author: Sergey Tkachenko

Sergey Tkachenko is a software developer who started Winaero back in 2011. On this blog, Sergey is writing about everything connected to Microsoft, Windows and popular software. Follow him on Telegram, Twitter, and YouTube.

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