UPDATE: This change has been reverted for now. It will take a couple days for the blocklist to be updated on everyone’s machine.
A while back, Mozilla had announced a plan to block all versions of Java by default. While that didn’t happen when Firefox 24 shipped, it has been done via an update to the blocklist. See bug 914690.
It’s unfortunate that this happened on the ESR, since Java is still essential for some enterprise applications (and apparently the entire country of Denmark).
I don’t have any information yet if you can use the permissions API to enable Java for necessary sites. For now, you might just have to turn off the blocklist by setting
extensions.blocklist.enabled to false.
UPDATE: You can also use the Click-To-Play Manager add-on to update the domain whitelist. I’ll be adding support for this into CCK2.