YouTube borked when users enable Firefox anti-fingerprinting

Firefox users have recently started to notice that YouTube does not display videos properly when they enable the browser's anti-fingerprinting technology for better privacy.

When the privacy.resistFingerprinting privacy feature is enabled in Firefox, the feature will make the browser more resistant to fingerprinting scripts. 

As fingerprinting can be used to track a user between different properties and even sites, it is a common feature suggested in Firefox privacy hardening guides.

A recent change on YouTube, though, is causing videos to have display problems when this feature is enabled.

As you can see from the image below, when resistFingerprinting is enabled, the video is cut off. This can be fixed by moving your mouse cursor outside the video, but in full-screen mode, it becomes a bit more difficult to remove the white cut off portion.

When the privacy.resistFingerprinting feature is turned off, the videos are displayed properly and not cut off as seen below.

BleepingComputer has been able to reproduce this issue in both Firefox 72 and the recently released Firefox 75, so this is not an issue caused by Mozilla.

In a Mozilla bug report and on Reddit, users have been able to track down the issue to the background being used for YouTube videos. When the resistFingerprinting feature is turned on, it changes the base64 encoded background-image being used for videos as explained below.

For those using an ad blocker, it has been found that you can fix the issue by adding the following rule:

www.youtube.com##.ytp-gradient-bottom

BleepingComputer has contacted Google about this issue but has not heard back as of yet.

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