I have been facing this technical incident for a long time, I wish i could report it for the concerned party for resolution. Microsoft Silverlight plugin is already installed but set to ask to activate in the adds-on & Plugin settings, Now once i need to use it shall notify on address bar corner by clicking activate Silverlight, but it only keeps as mentioned below & clicking the activate link is not working, the X button works one time then disappear, nothing happen only ESC keyboard button can remove. I wish i can help Mozilla for future updates Proudly & Warmest Regards to highly appreciated Mozilla. Thanking your cooperation with anticipation, we remain. Kindly be informed that the question above has been already sent on Google+ Firefox Community on 12th July 2015, here is the link for ease of reference: https://plus.google.com/+MOHAMADGHOUL81/posts/fFfJYv59P8h