When my users click 'view online' in explorer to play an MP4 video file without downloading it to local storage, a lightbox player loads in the browser with an install Silverlight message.
Installing Silverlight does nothing to remove the message, and it shouldn't be required anyway.
Clicking X to close the video, and then clicking on the very same video in the document library in the browser plays the video just fine with no need for Silverlight.
Microsoft support were lovely but failed to resolve the issue - their recommendation was to use IE11 instead of Edge or Chrome.
I suspect there is a way to disable the Silverlight lightbox player, but I haven't found it so far.