Steps to reproduce:
1. Open Add-ons Manager in Firefox.
2. Disable up-to-date Java plugin.
3. Click the link to the Plugin Check web page.
4. Page displays the following message:
"For your safety, Firefox has disabled your outdated version of Java. Please upgrade to the latest version."
It's the Java case of bug 734674.
*** Bug 786600 has been marked as a duplicate of this bug. ***
*** This bug has been marked as a duplicate of bug 790008 ***