Chinese Perapera-kun: Chinese Popup Translator
Simply put, this extension will allow you read Chinese on websites. This is useful for just getting around a site, or even MORE useful if you are studying Chinese. It works with both Simplified and Traditional characters, and also allows you to export words to a file to study later.
After installation, you can goto the "customize toolbar" menu and find the green book icon and put it on your firefox toolbar. When you are on a site with Chinese, simply click the green book icon and then put your mouse over Chinese words to view the reading and defintion.
In the extension options dialog you can set a place to save entries to, then when a the popup window with a definition is being displayed, if you press it will export the topmost entry to the file you designated.