~/.mozilla/firefox/myprofile.default/pluginreg.dat должен содержать такие строки для явы:

/usr/lib64/jvm/java-1.6.0-sun-1.6.0/jre/lib/amd64/libnpjp2.so:$
:$
:$
1238236087000:1:5:$
:$
libnpjp2.so:$
37
0:application/x-java-vm:Java::$
1:application/x-java-applet:Java::$
2:application/x-java-applet;version=1.1:Java::$
3:application/x-java-applet;version=1.1.1:Java::$
4:application/x-java-applet;version=1.1.2:Java::$
5:application/x-java-applet;version=1.1.3:Java::$
6:application/x-java-applet;version=1.2:Java::$
7:application/x-java-applet;version=1.2.1:Java::$
8:application/x-java-applet;version=1.2.2:Java::$
9:application/x-java-applet;version=1.3:Java::$
10:application/x-java-applet;version=1.3.1:Java::$
11:application/x-java-applet;version=1.4:Java::$
12:application/x-java-applet;version=1.4.1:Java::$
13:application/x-java-applet;version=1.4.2:Java::$
14:application/x-java-applet;version=1.5:Java::$
15:application/x-java-applet;version=1.6:Java::$
16:application/x-java-applet;jpi-version=1.6.0_13:Java::$
17:application/x-java-bean:Java::$
18:application/x-java-bean;version=1.1:Java::$
19:application/x-java-bean;version=1.1.1:Java::$
20:application/x-java-bean;version=1.1.2:Java::$
21:application/x-java-bean;version=1.1.3:Java::$
22:application/x-java-bean;version=1.2:Java::$
23:application/x-java-bean;version=1.2.1:Java::$
24:application/x-java-bean;version=1.2.2:Java::$
25:application/x-java-bean;version=1.3:Java::$
26:application/x-java-bean;version=1.3.1:Java::$
27:application/x-java-bean;version=1.4:Java::$
28:application/x-java-bean;version=1.4.1:Java::$
29:application/x-java-bean;version=1.4.2:Java::$
30:application/x-java-bean;version=1.5:Java::$
31:application/x-java-bean;version=1.6:Java::$
32:application/x-java-bean;jpi-version=1.6.0_13:Java::$
33:application/x-jinit-applet;version=1.3.1.21:Java::$
34:application/x-jinit-bean;version=1.3.1.21:Java::$
35:application/x-java-applet;jpi-version=1.4.2_04:Java::$
36:application/x-java-vm-npruntime:::$