The only part of Firefox that I really miss using is the awesome Rikaichan plugin.  I’ve managed to emulate it, poorly, by using a Json call to a dictionary I setup on my server.

To use this, drag the link below into your Bookmark bar.  Select some text and click the “Translate” button; you will get a translation, if it can find one.

Translator

I can imagine a few benefits to doing it this way, over the long term.  Mainly, keeping the information in a DB somewhere means someone can aggregate the information and provide you with additional services (“You are constantly misunderstanding X kanji”, for instance).  I can’t say anything about privacy implications.  

This is free for your use.  The backend is dirt simple and I’m using the Edict dictionary for the translations.  I’ll publish everything once I find a suitable place to do so.  Sorry for the speed (my server sucks – if anyone else has a better place, or even one that I can use Tokyo Tyrant with, I’d appreciate a message )

You can download the Javascript source here.  You can download the php backend code here.  I did it all in one sprint from 2 AM to 10 AM, so please don’t bother me about the lack of comments, I’m sure you are smart enough to understand what is going on.