I needed to install a Java plugin for Firefox under Ubuntu 9.04 (beta). This didn’t happen by itself when I installed sun-java6-plugin, but a quick search showed me what Eirik Hoem found out a year ago.

Or, as Karl Trygve said in a comment; messing about in /usr is usually not a good idea - the link could be made in /usr/lib/firefox-3.0/plugins, and the plugin would then be available for all users on the computer.

Linking the java plugin to Firefox (paths might vary a bit, depending on Java versions):

cd ~/.mozilla/firefox/.default/plugins
sudo ln -s /usr/lib/jvm/java-6-sun/jre/plugin/i386/ns7/libjavaplugin_oji.so

I didn’t have Icedtea installed, but I do use OpenJDK for development. Works now, at least. :D

I installed twhirl, to give it a twirl with twitter.

First issue was that URLs opened in Internet Explorer, instead of in Firefox. A bit searching lead me to throk.net for a possible solution, but Mozilla Firefox doesn’t show up under Set Program Access and Computer Defaults. It was mentioned that Flock doesn’t show up either, but Firefox 3 does.

Next try brought me to CNET’s Forums, where it was pointed out that IE still holds some file associations (*.url for one). Before I tried to mess around with that, I tried the suggestion of one LinuxDude; executing the following command from the Run dialog (Win key + R): firefox.exe -silent -setDefaultBrowser

This worked, but I can’t see any changes in Default Programs. I haven’t restarted yet, though.