HOWTO Install kana and kanji for Firefox on Debian Sarge

This article was first written in May 2004 for the BeezNest technical
website (http://glasnost.beeznest.org/articles/130).
This is a quick manual on how to install kana and kanji (Japanese writing) handling for the Mozilla-Firefox browser (and probably all other browsers) on Debian Sarge. I don't know whether the following is or isn't mandatory, but these steps were enough to give a good result.

Installing the "Languages" extension

* Note: this section has proven useless so I have moved it to the end of t