If you are using Linux and are facing problem with Java applets running correctly on Firefox, AND you have googled to the ends of the earth but still can't solve the problem, check this post out. The solution in my scenario is remarkably simple.
While I don't know the conditions that will create the problem, the solution is very simple.
In my case, I'm using openSUSE 10.3 with kernel 2.6.22, Firefox
126.96.36.199, and Java 1.5 (java-1_5_0-sun-1.5.0_update13-0.5). I'm
pretty sure that Java is installed correctly and the plug-in for
Firefox is also correct. You can check this by typing
about:plugins in the URL bar of Firefox. This will
bring up a page with the plug-ins that are installed for your Firefox.
So after checking that the Java plug-in is installed, I went to http://www.java.com/en/download/installed.jsp to check for a working plug-in. Doesn't work.
Naturally, I turned to Google. All results say the key to solving this problem is to create a symbolic link in Firefox's plug-in directory to Java's plug-in library. Through some investigation, I've found that there is a symbolic link that leads eventually to the plug-in: that is
/usr/lib/browser-plugins/javaplugin.so -> /etc/alternatives/javaplugin -> /usr/lib/jvm/java-1.5.0-sun-1.5.0_update13-sr2/jre/plugin/i386/ns7/libjavaplugin_oji.so
So what I did was to create a link to the same file above, this time the link is placed explicitly in Firefox's plug-in directory.
/usr/lib/firefox/plugins/libjavaplugin_oji.so -> /usr/lib/jvm/java-1.5.0-sun-1.5.0_update13-sr2/jre/plugin/i386/ns7/libjavaplugin_oji.so
Then I've read that I should remove duplicate links. Therefore I
deleted the link
Then a kind soul in SUSE's mailing list posted the simple solution.
Remove the .java hidden directory from your home directory:
rm -r ~/.java