If Java is installed but doesn't work, try these solutions: If the Java plugin does not appear in the Add-ons Manager, even though Java is installed, try each of the following, one at a time, and then reopen Firefox to see if that resolves the problem: With Firefox completely closed, delete (or rename) the file, located in the Firefox profile folder (it will be regenerated once you restart Firefox but any other plugins you may have disabled will be enabled).
Before anyone can help you in the IRC channel, please make sure that the following has been performed so that we can eliminate these as possibilities.
REPRODUCIBILITY : This bug can be reproduced always. Looks like the submitter is pointing towards the downloaded dmg files (for example, jre-8u73-macosx-x64.dmg) left behind on the system after the installation. Looks like the submitter is pointing towards the downloaded dmg files (for example, jre-8u73-macosx-x64.dmg) left behind on the system after the installation.
The "Java Deployment Toolkit" plugin is used by Java developers to detect your Java version and to deploy their Java applications and does not need to be enabled for Java to work.Java Runtime Environment updates can be downloaded from can be installed through the Java automatic update client, or can be manually updated through the Java Control Panel.Java Automatic Update Client: *Note: It is important to only have the latest version of the Java Runtime Environment installed because earlier versions may contain vulnerabilities.This can lead to a large accumulation of Java installers at ~/Library/Application Support/Java/.If keeping an installer after updates is desirable, then a checkbox should be presented in the updater.This article will help you install or update Java and get it working in Firefox.