Netflix recommend deleting the Silverlight plugin from the OS and reinstalling it. There are older cases here on the forums where this has been the solution.

The Netflix instructions are here: https://help.netflix.com/en/node/95. They also include some basic stuff like clearing your cache and cookies and disabling add-ons to see if some are or have become incompatible.

I could also find a Solution where Firefox needed to be switched to 32-bit mode in the OS, but this seems to have been a workaround in 2012 that is no longer necessary.

Thanks for your help. I carried out these steps and it worked briefly last night … yet seems to have reverted back to not working again today.

Alright - Silverlight is known for becoming corrupted, but rarely that quickly.

The next thing I would suggest is setting Silverlight to Always Activate in Firefox: go to about:addons, select the Plugins tab and choose Always Activate for Silverlight. This should make sure it starts, in case it's a page permissions issue and not an issue with Silverlight itself.

I noticed your browser version is 45.0. Please go to https://www.mozilla.org/en-GB/firefox/new/ and get the newest version, it should be 45.0.1 for your OS. You should also swing by https://www.mozilla.org/en-US/plugincheck/ just in case, but your plugins already look to be in order. Shouldn't be any sweeping changes in 45.0.1, but there was a performance regression fix in regard to sites like Youtube.

Updating the browser has seemed to fix it again. Here's to hoping it's a long-term fix this time!

Good to hear! Give it a week and get back to us so others may know if it was a lasting fix. ;)