After a long day of anger and speculation, Google has finally commented on the "artificial wait" that some Firefox users are encountering on YouTube. This 5-second delay, which is plainly visible in YouTube's code, is made to punish those who use ad blockers. It affects all browsers, not just Firefox.
Some YouTube users began encountering an odd video delay in mid-November. This phenomenon became controversial on November 19th, when a Reddit user accused YouTube of artificially slowing load times in Firefox. The logic was pretty straightforward. Delayed load times were only experienced in Firefox, and switching Firefox's user agent to Chrome automatically resolved the problem.
Additional evidence came in the form of a short snippet of code—setTimeout(function() { c(); a.resolve(1) }, 5E3);. This code, which is baked into YouTube, proves that the five-second delay is intentional. But Reddit users failed to see the big picture. This snippet of code cannot check which browser you're using. And when you look at the full function that this code is a part of, you'll find that it does not include any browser agent checks.
To support a diverse ecosystem of creators globally and allow billions to access their favorite content on YouTube, we’ve launched an effort to urge viewers with ad blockers enabled to allow ads on YouTube or try YouTube Premium for an ad free experience. Users who have ad blockers installed may experience suboptimal viewing, regardless of the browser they are using.
Before Google commented on this story, some people speculated that the five-second delay is associated with ad blocking. They were correct. When asked about the five-second delay, Google explained that "users who have ad blockers installed may experience suboptimal viewing, regardless of the browser they are using." This is corroborated by Firefox, which told 404 Media that the five-second delay affects all browsers.
As you may know, YouTube has spent the last few months cracking down on ad blockers. It wants customers to subscribe to YouTube Premium, which costs $13.99 a month (and includes a YouTube Music membership). Presumably, the five-second delay is a crude way of ensuring that ads actually play. Switching a browser's user agent "resolves" the problem because it refreshes the webpage—YouTube doesn't need to serve an advertisement after you refresh, so it doesn't enforce the five-second delay.
This is a pretty crude trick from Google. Ad-blocking services can get around the five-second delay with a simple filter. But Google is clearly hunting for new ways to discourage ad blocker usage, and a YouTube Premium subscription may be worth the money if you can't tolerate these annoyances. As for the whole Firefox thing—well, Google knowingly reduced YouTube's performance on non-Chrome browsers in 2018, so we can't blame anyone for jumping to conclusions.
Source: Google via 404 Media