There are 2 very nice extensions that provide furigana for web pages automaticaly:
This one provides furigana.
https://addons.mozilla.org/ja/firefox/addon/6178
You can choose your "kanji level" or edit it manualy. It seems very friendly, but the furiganas it generates are somewhat unreadable.
This one fixes it and gives very nice furigana. You can even adjust the font size.
https://addons.mozilla.org/ja/firefox/addon/6812
This one provides furigana.
https://addons.mozilla.org/ja/firefox/addon/6178
You can choose your "kanji level" or edit it manualy. It seems very friendly, but the furiganas it generates are somewhat unreadable.
This one fixes it and gives very nice furigana. You can even adjust the font size.
https://addons.mozilla.org/ja/firefox/addon/6812
Edited: 2008-10-27, 4:23 pm

I have a page about rikaichan without English glosses on my blog: