Users on Reddit and Hacker News are complaining that YouTube seems to have inserted an intentional five-second delay before video pages will load in Mozilla’s Firefox and occasionally some other browsers. YouTube tells The Verge that these users are right about the delay, but the browser has nothing to do with it — it’s part of the company’s efforts to quash ad blockers across all platforms.

“In the past week, users using ad blockers may have experienced suboptimal viewing, which included delays in loading, regardless of the browser they are using,” YouTube communications manager Christopher Lawton wrote in an email. Lawton wrote that disabling the ad blocker should resolve the issue, though users “may still experience a temporary delay in loading” until their browser has refreshed.

Lawton also said that users will keep seeing issues like this as YouTube’s ad-blocker detection methods improve.

The issue was initially reported as targeting Firefox users, but users online have said they’re seeing the delay in Chrome and Edge, too. Reddit and Hacker News users who’ve examined the code that appears to be causing the delay have said they see no indication that YouTube checks what kind of browser is in use. Mozilla’s senior brand manager Damiano DeMonte wrote in an email to The Verge that “there’s no evidence that this is a Firefox-specific issue.”

The five-second delay isn’t affecting everyone. A few of us at The Verge tried to recreate the issue, both on Mac and Windows machines. But whether logged into YouTube or not, using an ad-blocker or not, or going incognito or not, none of us saw the delay that’s being reported.

Google has made big moves on the ad-blocking front lately, and a lot of the thrust for that effort has been felt in YouTube, which started disabling videos for some viewers using ad blockers in June. YouTube confirmed last month that it had “launched a global effort” to get users to either enable ads or subscribe to its $13.99 per month ad-free Premium service. Lawton called ads “a vital lifeline for our creators.”

Last week, Google detailed a big change to Chrome that undermines uBlock Origin, one of the more popular ad-blocking extensions. Independent developers have been in an arms race with large companies that want to show ads for as long as there have been ads on the internet — and right now, Google seems serious about pushing back.