Mozilla released a new version of its Firefox web browser a moment ago. Firefox 127.0.2 fixes a long-standing playback issue on YouTube that was caused by the Google-owned property and not Firefox according to Mozilla's analysis of the issue.

For the past five or so months, some Firefox users were running into roadblocks regularly on YouTube. The full number of affected users is unclear. We published an article about the issue just last week.

Here are the details:

• It affected regular and live videos on YouTube, but not all of them.
• vp9 videos with a resolution of 1080 or higher were affected only.
• Affected users noticed an endless buffering issue.

Mozilla kept track of two main bugs. These were bug 1900191, which dealt with the live video problem, and bug 1878510, which dealt with the problem when watching regular videos on YouTube.

It took Mozilla some time to analyze the issue and come up with a solution. Core reasons for that were that the engineers could not replicate it at first, even when accessing the same videos on YouTube.

After a while, Mozilla engineer Alastor Wu discovered the root cause of the issue. He said that the issue has been caused by bad muxed VP9 bytestreams served by YouTube. The issue was caused by Google-owned YouTube therefore according to Mozilla and not a bug in the Firefox web browser itself.

Here is a quick summary of Wu's technical analysis of the issue: YouTube served bad video samples that overlapped with previously served ones. This should not happen, and is the cause of the problem. The overlapping caused Firefox to fail the calculation of the next sample, which would in the end trigger the endless buffering state. You can check the full comment by following this link.

The release notes state: "Fixed an issue where YouTube playback may experience stalling under certain conditions."

Closing Words

Mozilla did not mention why Chromium-based browsers were not affected by this. One possible explanation is that it is using a different kind of error-handling when running into the issue. Ultimately, it was Firefox and Firefox-based browsers that were affected by the issue only.

Affected Firefox users may upgrade the browser to the latest version immediately. This should fix the issue.

The easiest option to do so on the desktop is to select Firefox Menu > Help > About Firefox. This displays the current version and downloads the latest update that is available.

Mozilla released Firefox 127 earlier this month. It introduced a small number of changes, including security updates.

Do you use Firefox and play videos on YouTube using the browser? What has been your experience in the recent past?