Firefox is a major web browser used by many. A Firefox Java plugin crash can occur for several reasons, some of which are listed and discussed here.
The Firefox Java Plugin and Add-On Conflicts
The use of some plugins such as Adblock Plus or NoScript can result in a Firefox Java plugin crash. Because of this, users should check compatibility before installing new add-ons and extensions. In the event a Firefox Java plugin crash occurs, users should uninstall the add-on to restore functionality.
Before troubleshooting beyond removing errant add-ons, users should reinstall or update their Java runtime environment. This could be particularly important if Windows 7 is in use.
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Spoofed User Agent
A Firefox Java crash may result when using Firefox with a spoofed user agent. Web browsers use the user agent variable to tell host websites what kind of browser is requesting information from the site. By detecting the browser version used by a visitor, websites can optimize the visitor's experience by delivering content that leverages the features of that browser.
Firefox can manually change the user agent sent from their browser or use a user agent spoofer add-on that can be downloaded from the Mozilla Firefox Web site. This functionality can help users better access Web content that is optimized for other browsers.
The problem is that some users have experienced a crash of their Java plugin when spoofing user agents. This could be the result of the Firefox browser plugin expecting to see a Firefox user agent and not knowing how to respond when it sees a different value being sent between Firefox and the host website.
About the Java Plugin
The version of the Firefox Java plugin is revealed by typing "about:plugins" into the Firefox address bar. With the Java plugin version and vital information about all the other Firefox plugins that are installed, users can identify the likely cause of Java plugin crashes and keep tabs of all the add-ons and extensions that are currently in use on the system.
The Firefox Java plugin can crash if no value is found in the system registry at the following path: HKey Local Machine\Software\mozilla.org\CurrentVersion. If this key is missing from the registry, users should attempt to reinstall the Firefox Web browser.
Avoiding a Firefox Java Plugin Crash
To avoid a Firefox Java plugin crash, users should eliminate all plugins that use Java from the Firefox plugin directory prior to installing an update Java runtime environment.
Users that experience issues with the Java plugin for Firefox in the Windows version of the program should remove or avoid the Adblock Plus and NoScript add-ons. Also, add-ons that spoof the user agent variable should also be eliminated as part of the solution for crashes of the Firefox Java plugin.
Finally, users who are experiencing problems with their Java plugin under the Firefox browser environment should use Regedit to verify that the CurrentVersion key is present in the Mozilla hive under HK Local Machine\Software\mozilla.org.