It seems like there is potentially a lot of room for the differences to be in the way Netflix is using the technology vs. an inherent different in picture quality using each Silverlight and Wildvine.
As someone who isn't supertechnical, I am not sure if any of these reasons are truly possible reasons, but it seems like there could some reason similar to them, at least hypothetically:
Netflix is known to encode a lot of its catelog at several bitrates per movie or episode, delivering the end user a higher bitrate if they have a faster congestant and Netflix is less congested, and a lower bitrate if they have a slower connection and Netflix is more congested, something that sometimes results in changes to picture quality in either or both directions even as one is watching.
If you've noticed a show or movie starting blocky like a old Nintendo game and gradually increasing in definition, that's what's going on. Its also building a small buffer.
What if one codec takes less bandwidth than the other, alllowing Netflix to give you their better quality version of that codec more often?
What if Netflix arbitrarily maintains its library differently depending on the codec? For example, of one codec offers things at 420p or 1080p, and the other has 440p and 720p available. In some situations, one codec would look better and in others, the other codec, for reasons having nothing to do with the codecs themselves.
Its also possible that Netflix's infrastructure is more optimized towards Silverlight, having been using that technology longer. Its also possible that people's home infrastructure is more optimized for it- for example, using a Windows PC, which is made by the same company as Silverlight, or a certain chip architecture (i.e. Intel vs ARM or whatever the case may be). There are also a bunch of hardware boxes that are used with TVs that may have varying capabilities even within the same line, as well as phones and devices that have different capabilities. The thing is, though- ultimately, in the long run, both Netflix's internal hardware and software, and that of the end user is destined to eventually turn over as hardware breaks or becomes obselete and software gets updates or is changed to something considered more advanced.
In any event, all that aside (And not just because I'm probably wrong
), it seems like there is one very good reason for Netflix and other streaming providers to switch off Silverlight:
Microsoft has ended development on Silverlight except for patches and big fixes, and has plans to stop even issuing those eventually. Consequentially, Chrome and Firefox have stopped officially supporting it, and Edge has never and will never support it.
Silverlight lost the platform war on two fronts, to the older Flash initially, and now increasingly to the newer HTML5-based DRM solutions. Many times the loser in the platform war is actually the better technology- some people will staunchly maintain that Laser-Discs were superior to DVDs and that HD-DVD was superior to Blue-Ray. But what can you do? They stopped putting out new movies in the losing formats eventually, and new players, so people who who were determined to stick with them were limited to what they already had plus what they could buy used, with replacement players and discs becoming increasingly hard to find and expensive to obtain, and even if one had unlimited time and money to go after the used stuff to replace, repair, and expand what they have, they'd never be able to buy new movies made after a certain date in those formats.
Eventually, there isn't going to be a streaming service that streams using Silverlight, and eventually any browser offering it as a plug-in will be pirating unsupported old versions, after Microsoft finishes phasing it out and allowing for its distribution.
And, in the interest of looking on the brightside- Silverlight as far as I know never ran properly on Linux, whereas EME should mean that Netflix and the like can offer streaming on Linux through the native browser implentations in Firefox and Chromium. This also could make things a bit easier on streaming boxes of the future that have some sort of Linux at their core.
The only real problem I have with the DRM aspect of EME is that it may be prohibitively expensive for smaller browsers, reducing user choice in that field and the ability of smaller browsers to compete.
I expect some sort of DRM to be on what is essentially a rental subscription service- because you're renting, not buying, and they have to at least try to enforce that somehow or you've defacto bought tens of thousands of hours of ebtertainment for $10 as a one-time fee, which isn't a financially workable model. What bothers me more from a principle perspective is when someone sells a video at full price in DVD format or tied to a specific website and platform with DRM- if one buys something specific at full price, they should be able to male archival copies for personal use and use it when they want on any device or OS they can get to play it- so there shouldn't be DRM on items for sale. But a monthly all you can stream rental service? I'm cool with DRM on that.
The potential of smaller browsers being potentially unable to use this and compete with the larger browsers bothers me, but has anyone actually checked with the people who handle the DRM and asked about allowing their small browser to be allowed to try to implement a version of it? I always hear it assumed that it wouldn't be allowed and that the powers that be behind it would demand some ridiculous sum of money that is more money than small browser companies themselves would make in a million years, but I never here any word about actual inquries. What if they would be happy to let small browsers browsers implement it and only charge on a per-user or per-download basis that would scale and make the total cost much less than they charge big browsers with lots of users?
And, of course, with Pale Moon specifically, cost may be a non-issue because last I heard Pale Moon was taking the stance that they didn't want it at any price, or even for free. If that's changed, I would suggest at least reaching out to whomever controls EME DRM and asking what the price would be for a browser with a smaller number of users owned by a small business that can't match Google in terms of a flat fee. Maybe you'd get a surprisingly positive response.
Also, it may be that forks that stay closer to the browsers from wherence they came are just able to carry some of the implementations over with the rest.