Copied from the How to allow Java on trusted sites article discussion:
/kb/how-to-enable-java-if-its-been-bl.../5171
AliceWyman said
.... I agree that the content included in http://kb.mozillazine.org/Java#If_the_Java_plugin_does_not_appear_in_the_Add-ons_Manager_even_though_Java_is_installed should be added to a SUMO KB article on Java issues but I think it belongs under the "Troubleshooting" section of the Use the Java plugin to view interactive content on websites article.
We should also add a link to the Use the Java plugin to view interactive content on websites article in this article, probably in the Intro, for users who need more help with Java.
I'll see if I can get to it when I have the time. You (or anyone else) could also try making the revision if you feel up to it.
Here's the information that's in MozillaZine's Java article, including references. (It will need to be edited to remove references and links that are internal to MozillaZine's KB).
If the Java plugin does not appear in the Add-ons Manager even though Java is installed
If the Java plugin does not appear in the Add-ons Manager, even though Java is installed, first do the following before reinstalling Java or trying other solutions:
- Open the Firefox profile folder or the SeaMonkey profile folder, then completely close Firefox or SeaMonkey and delete (or rename) the "pluginreg.dat" file. A new pluginreg.dat file will be generated when you restart the browser. Any plugins you may have disabled in the Firefox or SeaMonkey Add-ons Manager will be re-enabled. https://support.mozilla.org/en-US/que.../944191?page=5#answer-397074
- On Windows or Mac OS (OS X 10.7.3 and above), If Java 7 is installed, make sure that "Enable Java content in the browser" is selected in the Java Control Panel's Security tab (see below).
- On Mac OS (OS X 10.7.3 and above) the Java 7 plugin will only run in 64-bit browsers so confirm that you aren't running Firefox or SeaMonkey in 32-bit mode. Open the Applications folder in Finder, control-click (right-click) the Firefox.app or SeaMonkey.app and select "Get Info". Make sure the box in front of "Open in 32-bit mode" is not checked (if it is, remove the check-mark). http://java.com/en/download/faq/java_mac.xml#sysreq https://support.mozilla.org/en-US/que.../975269
- On 64-bit Windows, if you only have the 64-bit version of Java installed, the Java plugin will not be available since current Firefox and SeaMonkey releases are 32-bit browsers. You'll need to install the 32-bit Java version (see below). http://www.java.com/en/download/faq/java_win64bit.xml
- On Windows, if the Java(TM) Platform SE plugin is not detected and you recently updated to Java 7 Update 10 or Update 11, uninstall JavaFX, if installed (see below).
- On Windows, Mozilla browsers use plugin scanning to locate installed plugins in locations external to Firefox or SeaMonkey. Java and other plugins in directories specified in the Windows registry for PLIDs will not be detected if the preference plugin.scan.plid.all has been set to "false". To resolve, open [[about:config]] and reset the preference to "true" (the default value), then restart Firefox or SeaMonkey. https://support.mozilla.org/en-US/que.../938258#answer-371433
<snip>
Enabling and disabling Java from the Java Control Panel
Applies to Windows or Mac OS X 10.7.3 and above
Starting in Java 7, the Java Control Panel includes the Security option, "Enable Java content in the browser", which is selected by default. De-selecting this option will prevent Java applets from running in any browser and the Java plugin will no longer appear in the Firefox or SeaMonkey Add-ons Manager or [[about:plugins]] list. To view or change this option, click the Java icon in the Windows Control Panel or Mac OS X System Preferences to open the Java Control Panel, then select the Security tab. See this Java Help page for details. http://www.oracle.com/technetwork/jav.../7u10-relnotes-1880995.html http://docs.oracle.com/javase/7/docs/.../jcp.html#security http://www.java.com/en/download/help/jcp_security.xml
Copied from the [[How to enable Java if it's been blocked]] article discussion:<br>
[/kb/how-to-enable-java-if-its-been-blocked/discuss/5171] <br>
''AliceWyman said''
<blockquote> .... I agree that the content included in http://kb.mozillazine.org/Java#If_the_Java_plugin_does_not_appear_in_the_Add-ons_Manager_even_though_Java_is_installed should be added to a SUMO KB article on Java issues but I think it belongs under the "Troubleshooting" section of the [[Use the Java plugin to view interactive content on websites]] article.
We should also add a link to the [[Use the Java plugin to view interactive content on websites]] article in this article, probably in the Intro, for users who need more help with Java.
I'll see if I can get to it when I have the time. You (or anyone else) could also try making the revision if you feel up to it.
</blockquote>
Here's the information that's in MozillaZine's Java article, including references. (It will need to be edited to remove references and links that are internal to MozillaZine's KB).
===If the Java plugin does not appear in the Add-ons Manager even though Java is installed===
If the Java plugin does not appear in the Add-ons Manager, even though Java is installed, first do the following before reinstalling Java or trying other solutions:
*Open the [[Profile folder - Firefox |Firefox profile folder]] or the [[Profile folder - SeaMonkey |SeaMonkey profile folder]], then [[kill application|completely close]] Firefox or SeaMonkey and delete (or rename) the "pluginreg.dat" file. A new pluginreg.dat file will be generated when you restart the browser. Any plugins you may have disabled in the Firefox or SeaMonkey Add-ons Manager will be re-enabled. [https://support.mozilla.org/en-US/questions/944191?page=5#answer-397074]
*'''On Windows or Mac OS''' (OS X 10.7.3 and above), If Java 7 is installed, make sure that "Enable Java content in the browser" is selected in the Java Control Panel's Security tab ([[#Enabling and disabling Java from the Java Control Panel|see below]]).
*'''On Mac OS''' (OS X 10.7.3 and above) the Java 7 plugin will only run in 64-bit browsers so confirm that you aren't running Firefox or SeaMonkey in 32-bit mode. Open the Applications folder in Finder, control-click (right-click) the Firefox.app or SeaMonkey.app and select "Get Info". Make sure the box in front of "Open in 32-bit mode" is not checked (if it is, remove the check-mark). [http://java.com/en/download/faq/java_mac.xml#sysreq] [https://support.mozilla.org/en-US/questions/975269]
*'''On 64-bit Windows''', if you only have the 64-bit version of Java installed, the Java plugin will not be available since current Firefox and SeaMonkey releases are 32-bit browsers. You'll need to install the 32-bit Java version ([[#On Windows|see below]]). [http://www.java.com/en/download/faq/java_win64bit.xml]
*'''On Windows''', if the '''Java(TM) Platform SE''' plugin is not detected and you recently updated to Java 7 Update 10 or Update 11, [[#Uninstall_JavaFX |uninstall JavaFX]], if installed (see below).
*'''On Windows''', Mozilla browsers use [[plugin scanning]] to locate installed plugins in locations external to Firefox or SeaMonkey. Java and other plugins in directories [https://developer.mozilla.org/en-US/docs/Adding_Extensions_using_the_Windows_Registry#Plugins specified in the Windows registry] for [http://www-archive.mozilla.org/projects/plugins/plugin-identifier.html#definitions PLIDs] will not be detected if the preference '''plugin.scan.plid.all''' has been set to "false". To resolve, open [[about:config]] and reset the preference to "true" (the default value), then restart Firefox or SeaMonkey. [https://support.mozilla.org/en-US/questions/938258#answer-371433]
<snip>
===Enabling and disabling Java from the Java Control Panel===
''Applies to Windows or Mac OS X 10.7.3 and above''
Starting in Java 7, the [http://docs.oracle.com/javase/7/docs/technotes/guides/jweb/jcp.html Java Control Panel] includes the Security option, "Enable Java content in the browser", which is selected by default. De-selecting this option will prevent Java applets from running in any browser and the Java plugin will no longer appear in the Firefox or SeaMonkey Add-ons Manager or [[about:plugins]] list. To view or change this option, click the Java icon in the Windows Control Panel or Mac OS X System Preferences to open the Java Control Panel, then select the Security tab. See [https://www.java.com/en/download/help/enable_panel.xml this Java Help page] for details. [http://www.oracle.com/technetwork/java/javase/7u10-relnotes-1880995.html] [http://docs.oracle.com/javase/7/docs/technotes/guides/jweb/jcp.html#security] [http://www.java.com/en/download/help/jcp_security.xml]