[Affected versions]: Fx 54.0.3, 55.0b6, 56.0a1 [Affected platforms]: Windows 7 x86 Windows 8 x86 [Steps to reproduce]: 1. Open Firefox. 2. Go to "https://www.netflix.com/". 3. Click to play a video. [Expected result]: The video is played using pre-installed plug-ins. I have Widevine Content Decryption Module 1.4.8.903 set to Always Activate. [Actual result]: Firefox ask for Microsoft Silverlight plug-in to be installed. [Regression range]: Last good: build id=20161003030438 (52.0a1) First bad: build id=20161004030204 (52.0a1) https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=6a14bfe49c90a45a832f2697b5daadd4355d2616&tochange=c57e289647966c2789566768e78a800bc670e290 The pushlog points to this bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1269807 [Notes]: Win 10 x86 and 64-bit Windows versions are not affected.

I tried reproducing this bug on my Windows 10 x64 machine (with Widevine version 1.4.8.903) by overriding my User-Agent header ("general.useragent.override" = "Mozilla/5.0 (Windows NT 6.1; rv:52.0) Gecko/20100101 Firefox/52.0"), but I couldn't reproduce it. I don't have a Windows 7 or 8 x86 machine. Maybe Netflix is trying to feature detect something and not just sniffing the User-Agent header, so my User-Agent override didn't work?

Timea: Do you have a user agent spoofer installed? If you navigate to http://pearce.org.nz/ua.html what string do you see?

There is no user agent installed on the machines we reproduced this. Win 8 result on http://pearce.org.nz/ua.html: Mozilla/5.0 (Windows NT 6.2; rv:55.0) Gecko/20100101 Firefox/55.0 On this system the issue no longer reproduces on Firefox 55 beta 6, beta 7 and latest Nightly 56.0a1. I saw instead the notification saying that there is an unsent crash report: https://crash-stats.mozilla.com/report/index/ac3529b6-1048-4175-b458-c289f0170711 - the signature is related to video playing and could be the reason for which Netflix is now working. Win 7 result on http://pearce.org.nz/ua.html: Mozilla/5.0 (Windows NT 6.1; rv:55.0) Gecko/20100101 Firefox/55.0 The issue still reproduces here on Firefox 55 beta 7, beta 8 and latest Nightly 56.0a1.

Reproduced the issue on windows 7 x64 Build ID 20170730100307 as following: On Win 7 x 64 with Nightly build 64: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0 Widevine Content Decryption Module 1.4.8.970 set to Always Activate. - When trying to watch a video on Netflix via Widevine - error returned: Error code: F7355-1204 (see image One) - When trying to watch a video on Amazon via Widevine - "Microsoft Silverlight is not installed" message displayed (see image Two) On Win 7 x64 with Nightly build 32: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:56.0) Gecko/20100101 Firefox/56.0 Widevine Content Decryption Module 1.4.8.970 set to Always Activate. - When trying to watch a video on Netflix via Widevine - "Silverlight is required to play " returned (see image Three) - When trying to watch a video on Amazon via Widevine - "Microsoft Silverlight is not installed" message displayed (see image Two)

Deac Alin: What does https://www.youtube.com/html5 show? Do you have ticks for H.264? Sometimes the error you're seeing happens on versions of Windows without AAC audio decoders installed. Are you using an "N" variant of Windows? Are you using an "Enterprise" or Server variant of Windows?

Also, does the video at https://pearce.org.nz/video/h264.html play on your test machine?

Hi Chris, 1. https://www.youtube.com/html5 shows everything checked except: MSE & H.264 and H.264 (red exclamation mark) 2. I am using Windows 7 Professional N variant x 64 Service pack 1. 3. When trying to access https://pearce.org.nz/video/h264.html returns the following message: "Not Found The requested URL /video/h264.html was not found on this server. Apache/1.3.41 Server at pearce.org.nz Port 443" I hope this information is helpful and do not hesitate to ask if further info is required. Thank you

(In reply to Deac Alin from comment #7) > Hi Chris, > > 1. https://www.youtube.com/html5 shows everything checked except: MSE & > H.264 and H.264 (red exclamation mark) > 2. I am using Windows 7 Professional N variant x 64 Service pack 1. > 3. When trying to access https://pearce.org.nz/video/h264.html returns the > following message: > "Not Found > The requested URL /video/h264.html was not found on this server. > Apache/1.3.41 Server at pearce.org.nz Port 443" Sorry, that should have been http:// not https://. My webhost doesn't support letsencrypt yet. :( > I hope this information is helpful and do not hesitate to ask if further > info is required. Thank you Yes. You've confirmed my suspicion that your machine isn't correctly configured for playing media. If you install the "Media Feature Pack for Windows N", this should work. https://www.microsoft.com/en-nz/download/details.aspx?id=48231

But couldn't Netflix show a more appropriate warning?