rikaichan is a popup Japanese-English/German/French/Russian dictionary extension for Firefox, Thunderbird and Seamonkey.

Features:

* Simple to use, just hover the mouse on top of a Japanese word. * Automatically de-inflects verbs and adjectives. * Has an optional toolbar that allows you to manually type the word to lookup. * Detailed kanji view shows meaning/keyword in English, on/kun readings, and other information. * Hiragana, katakana and half-width katakana are treated the same making it possible to lookup stylized/emphasized words.