Mozilla has announced that it will be dropping support for most web plugins by end of 2016. This includes the likes of Java and Silverlight, although Flash will continue to be supported.
Web plugins used to be an integral part of the web experience, mostly to play back multimedia content, which wasn't natively supported by either the web or the browsers. However, with the advent of HTML5 and browsers that can render full 3D games plugins have become increasingly irrelevant. Not to mention they were never particularly good, and offered poor performance and battery life and also increased security risk.
Other browsers such as Chrome and Edge have already dropped support for plugins. Chrome even disables non-essential Flash content by default. Mozilla's end of 2016 date is perhaps a bit too far from now but at least the company has decided to drop support for plugins. And upcoming platforms such as 64-bit Firefox for Windows will not have support for plugins out of the box.
No... they won't exist anymore. Those technologies are reaching their end, giving way to HTML5.
Good. Then all of these features(flash, java, silverlight) will be built-in instead of plug-in.. Should increase the stability if built in