NPAPI plug-ins are antiquated and other browsers are removing support for plug-ins and sunsetting Flash.
I couldn't find another issue for this, so I'll just put it here.
NPAPI plugins are a huge security threat and the modern web has almost completely moved past them already.
You can't even use any plug-in but Adobe Flash on Firefox, and Chrome blocks its pepper Flash player in very nearly all cases. The major browser vendors are sunsetting NPAPI and Flash too. Microsoft Edge has never supported plug-ins.
I don't know what the maintenance burden of supporting NPAPI in Epiphany is, but one of the stated goals of Epiphany is to be simple and do things that make sense. Java on the web is dead. Flash is nearly dead. (Largely supplanted by HTML 5.) Epiphany has never needed Adobe Reader. All NPAPI plug-ins represent a huge security risk to the user. Flash alone gets more CVEs thn some entire operating systems in any given year, and Adobe has it in bug-fix only mode with a plan to stop even providing security updates in 2020. Aside from security issues, two of the historical plug-in nuisances have been really large and annoying advertisements and failing to truly integrate with the browser that hosts them. Flash has never existed in a big way on mobile devices, as Steve Jobs pointed out in "Thoughts on Flash", the user experience would have been simply awful. Android tried supporting it but gave up a long time ago, and it was awful.
Is it time to consider disabling NPAPI plug-in support for Epiphany? I currently have support for it unchecked even though I have no such plug-ins on my computer.