Hi,
I'm running SliTaz 3.0 stable with Firefox 3.5.7.
I also installed a Firefox distribution in 3.6.x and in 4.x version. I downloaded the tarball from official Mozilla website, untared them into an "apps" subfolder in my home, running them by accessing their "firefox" respective binary ($HOME/apps/firefox-3.6/firefox and $HOME/apps/firefox-4/firefox).

I installed Java on my machine with java-6-jre and then icedtea6-jre (not sure this one was absolutely necessary).
Java plugin does exist and is recognized and usable in native 3.5.7 Firefox distribution, but *not* in my additionnal local Firefox distributions.
Then I made a "plugins" subfolder in each distribution folder and made a symbolic link to the plugin:
libjavaplugin_oji.so -> /usr/lib/java/jre1.6.0_17/plugin/i386/ns7/libjavaplugin_oji.so (as it was already done for system-wide Firefox distribution in /usr/lib/mozilla/plugins and /usr/lib/firefox-3.5.7/plugins.
Each link belongs to root:root and has all permissions on: chmod a+rwx.
Of course, the original plugin file (in /usr/lib/java/[...]) has right permissions too (same as above).

What else should I do ? Is it known to be able to work ?
Thanks,

-Babaorum