hello nju001, for more information about this issue please refer to Why do I have to click to activate plugins?

I already understood about activating plugins and I understood about vulnerabilities. The message window I am asking about simply did not make any sense: "Do this. Don't do this." If the Web site was requesting that Java Deployment Toolkit to be activated, the message should have said, "This site is requesting you to activate Java Deployment Toolkit plugin. This plugin has known vulnerabilities and Firefox recommends that you not activate it."

See all of the following:

1. Java Deployment Toolkit is only needed by Java developers and users who edit Java applets on web pages.
   • Most users do not need Java Deployment Toolkit enabled.
   • Java will work without Java DT enabled
   • See - https://www.java.com/en/download/faq/deployment_toolkit.xml
2. You appear to have Java 6u45 installed; it is no longer maintained by Oracle/Java
   • Java 6 not longer maintained/updated by Java - https://www.java.com/en/download/faq/java_6.xml
3. Why Mozilla disables Java Deployment Toolkit - https://addons.mozilla.org/en-US/firefox/blocked/p428
4. Update Java (ver 7u40 is current) - https://support.mozilla.org/en-US/kb/use-java-plugin-to-view-interactive-content

Other - Check your Plugins and update as needed.

1. Check your Plugins - https://www.mozilla.org/en-US/plugincheck/
2. Shockwave Flash 11.7 r700
   • https://support.mozilla.org/en-US/kb/keep-flash-up-to-date-and-troubleshoot-problems
   • https://support.mozilla.org/en-US/kb/install-flash-plugin-view-videos-animations-games
   • Test Flash version here - http://helpx.adobe.com/flash-player/kb/find-version-flash-player.html (Items 1 and 2 show your installed version, Item 3 lists latest version for various systems)
3. Adobe Shockwave for Director Netscape plug-in, version 12.0.2.122
   • http://kb.mozillazine.org/Shockwave
   • Download and SAVE installer, close all browsers, run the installer - https://www.adobe.com/shockwave/download/alternates/
   • Check Shockwave Player version here - http://www.adobe.com/shockwave/welcome/

EDIT
IMPORTANT: You seem to be using Firefox 17 which is outdated and vulnerable to hackers

Firefox 24.0 was released 09/17/2013. Please Update

• https://support.mozilla.org/en-US/kb/update-firefox-latest-version

I was with the same problem and this is how I solved the issue:

-In the Location bar, type about:config and press EnterReturn. "This might void your warranty!" warning page may appear. Click I'll be careful, I promise! to continue to the about:config page.

-Search for the preference: dom.ipc.plugins.java.enabled

-Click 2 times on this preference. It'll change the value from false to true.

-It's done! I'm not sure if it's going to work with everyone but worked for me immediately. No need to restart the Firefox.

Good day! Guazevedo

Do not confuse the Java plugin that runs the applets and the Java Deployment Toolkit plugin that is useful for Java developers, but isn't needed for normal users.

• http://www.java.com/en/download/faq/deployment_toolkit.xml

The Java plugin is not supposed to run in a plugin-container process, so setting the dom.ipc.plugins.java.enabled pref to true is not recommended and best is to leave this pref at its default value false.

I've tried all things written in the firefox community and any one solved my problem. How do I uninstall the Java Deployment Toolkit manually?