If you do any sort of Japanese reading on the Internet, you’ll want these two Firefox extensions:
XHTML Ruby Support Furigana Injector
The first one adds proper ruby (a.k.a. furigana, in the case of Japanese) support to Firefox. The second one is more interesting: it adds furigana to kanji on websites that don’t have it, making it much easier to read Japanese text.
An interesting side-effect of having proper ruby support in Firefox is that the times in blogger look quite odd, with the full date above them.