Google disrupted YouTube video playback on Firefox, again

Being a Firefox user can be quite difficult these days. Besides getting regular prompts to switch to the browser of a mega-corpo, excuse the Cyberpunk slang, it is predominantly issues with certain websites and services that Firefox users have to battle against.

One of the latest examples comes from Google-owned YouTube. Some Firefox users noticed playback issues on YouTube for several months. These affected high resolution videos only, from 1080p and up. To make matters worse, no clear pattern could be identified.

Some videos played fine, others would stop abruptly when they ran out of buffer. The issue affected Firefox only (and maybe Firefox forks). All Chromium-based browsers were not affected by it.

Investigation points at YouTube as the culprit

After months of investigating the issue, Mozilla finally found a fix for the issue. This fix will be released as Firefox 127.0.2 later this month, as it did not make it into the Firefox 127.0.1 release of today.

The fixing took longer than expected, as it was difficult to reproduce the issue.

According to Mozilla engineer Alastor Wu, the issues was caused by Google's YouTube service and not by a regression in Firefox.

He writes on Bugzilla: "This problem is triggered by bad muxed VP9 bytestream served by Youtube, so it's not a regression on our side, this issue can also be reproduced on old versions Firefox".

In other words: Google introduced the issue on YouTube. While there is no evidence that Google did so deliberately, it is clear that the outcome is catastrophic for affected Firefox users and Mozilla.

Affected users might have blamed Firefox for the issue. Some may even have switched to a Chromium-based browser, as these worked without any issue.

Not the first time, likely not the last

Back in 2018, Firefox engineers complained on Twitter (now-X), that YouTube was loading five times slower in non-Chromium browsers. The issue affected Firefox and the old version of Microsoft Edge back then.

Google was using a deprecated API on YouTube that only Chromium supported. This left Firefox, Edge, and other non-Chromium browsers standing in the rain.

In 2023, Firefox users started to notice another issue on YouTube. Videos would take longer to load, which only affected the browser and not Chromium-based browsers. Microsoft, having switched Edge to a Chromium-base by then, was not affected by the issue.

One potential explanation

While some may cry foul-play immediately, there are other explanations. Here is one:

Google may test changes only in Chrome / Chromium, and not in Firefox. Or it may test changes only cursory in other browsers. This could lead to bugs that are not noticed when new changes are implemented.