YouTube slows loading on Firefox

YouTube has started cracking down on ad blockers, and that now includes slowing down load times for anyone with an ad blocker installed on any browser.

Updated 11/21: In an updated statement to 9to5GoogleYouTube says ad blocker detection is causing “suboptimal viewing” on, including this new slower loading behavior.

Ads are a vital lifeline for our creators, helping them run and grow their businesses. This is why using ad blockers violates YouTube’s terms of service. We’ve been urging users to allow ads on YouTube or try YouTube Premium for an ad-free experience for some time. Over the past week, users using ad blockers may have experienced suboptimal viewing, including loading delays, regardless of which browser they are using. Users who have uninstalled their ad blockers may still experience a temporary loading delay and should try refreshing their browser.

Although this was first noticed with Mozilla Firefox, as described below, YouTube states that its ad blocker detection does not target specific browsers and that this behavior can be observed on any browser with an ad blocker installed.

Our original coverage and YouTube’s previous statement follows:

Loading is something many people do daily, but recently this process has been strangely slow for some, especially on Firefox.

Redditor u/vk6_ posted a video that shows YouTube loading on Firefox with a significant delay. For a few seconds, the page is virtually blank, with background elements displayed but no content to accompany it. After a few seconds, the page loads as usual.

One might assume that this is simply a connection issue, but the video makes it pretty clear that this is a Google choice. When you spoof Firefox’s user agent as Chrome, YouTube loads completely normally. There is no waiting time and the entire loading is radically faster.

At first glance, this really seems like clear evidence that this is a choice on Google’s part, and there could be there even more. Another user found code on that displays a “timeout” function in the script that forces users to wait five seconds before the page loads. However, some believe this could be linked to the crackdown on ad blockers. The code itself doesn’t appear to point to Firefox in particular, but some users have found that using a filter for this code seems to fix load times.

It’s also worth noting that we tried this the other way around. Spoof Chrome to act like Firefox does not put this deadline into effect.

But it’s hard to say anything with certainty.

Update: In response to 9to5GoogleGoogle pointed to ad blockers as the apparent reason for the slowdown, saying that “users with ad blockers installed may experience suboptimal viewing regardless of the browser they use.”

To support a diverse ecosystem of creators globally and enable billions of people to access their favorite content on YouTube, we launched an effort to encourage viewers with ad blockers enabled to allow ads on YouTube or try YouTube Premium for an ad-free experience. Users with ad blockers installed may experience suboptimal viewing regardless of which browser they use.

While this doesn’t answer the question of why loading was faster when Firefox was masquerading as Google Chrome, it does fit with the fact that this particular user had an ad blocker installed, as is barely visible in the video in the top bar of Chrome. In our spoofing tests of Chrome and Firefox, in particular, no such ad blocker was installed.

If you see loading slowly on Firefox and you not have an ad blocker installed, let us know in the comments below.

The reasoning behind this is unclear, but it comes at a far from ironic time. Amid the crackdown on ad blockers and Chrome’s removal of Manifest V2 extensions (which will break some ad blockers), Firefox has become a go-to place for many people.

The other explanation could simply be a technical bug, but it’s hard to say what it is. Firefox runs on the Gecko browser engine, unlike the more widely used Blink on Chrome, Edge and others, and WebKit, which is used on Safari, but spoofing the browser with an extension doesn’t change the engine used, which, again once suggests it has something to do specifically with Firefox. Our own Kyle Bradshaw suggests it could be as simple as the codebase used for the Gecko engine having a testing delay that accidentally made it to production. The fact that this doesn’t happen when spoofing Chrome to act as Firefox supports the idea that this is more of a technical issue.

Regardless, this is a very frustrating and pretty crazy topic to see.

Google has so far not acknowledged the problem.

More on YouTube:

Update: This article has been updated to reflect testing where spoofing Chrome to act like Firefox does not show the same delay.

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