Firefox privacy settings breaks Netflix

Mozilla Firefox has been a privacy-first browser for years and is excellent. Recently I found my way to (yet another page on the excellent) page on the Arch wiki, about Firefox privacy. There I found out about the following setting (which can be modified in about:config) to increase/enhance your privacy to resist fingerprinting even more:


The wiki page includes a warning (which, I hoped for, would have been exaggerated). It made me find a bug in the website of a primary school, but also broke DRM playback for a major streaming service. On the upside: it has worked fine for me for lots of other websites.

the bug

The primary school of my children uses Social Schools (a hosted webportal for parents). So recently we had to plan a meeting with a teacher via that portal, which went fine. At least that was what we thought, until the teacher told us (by sheer chance, because my wife spoke to her casually about the meeting) that it was planned for an hour later.

So I went forth and went digging around. The webinterface still showed us the “wrong” time, but the confirmation e-mails stated the “correct” time. It was an hour off, which is weird. The offset is close enough not be noticed at a glance, since I honestly did not check the confirmation mail diligently and did not notice it.

In the end, it appears that the webportal uses Javascript to detect the current timezone. We live in ‘UTC+1’, but with privacy.resistFingerprinting: true that became ‘UTC’ for their front-end.

Of course I filed a bugreport with them and hope for a fix in the future.

the DRM playback

A while ago I flushed my browser profile and since then, I did not get netflix playback working again. One of the errors I got was:


As a temporary workaround (did not want to debug a lot at the time and already tried disabling plugins etc.) I just used another browser and worked around the issue. But when I was confronted with the bug above, I remembered this issue and decided to test it. And yes, if you enable privacy.resistFingerprinting, your Netflix playback will break.