This is an easy tutorial to add useful dictionaries to Firefox search box.
Go to http://mycroft.mozdev.org/index.html
Copy-Paste these words in the search box, and add the search engines:

yahoo! dictionary jp

kenkyusha japanese dictionary

alc.co.jp

reviewing the kanji

Of course you can add many more search engines, like google, youtube, wikipedia, etc

On Google Chrome, simply right-click the URL bar to find the options to add search engines directly to it.

For many search sites firefox lets you add them to the search box with one click, too (the little triangle glows blue or something like that). Also you can set a code for each search engine (like 'g' for google, 'wj' for Japanese wikipedia) which you can use in the address bar. For example you'd only have to type 'wj 芥川龍之介' to search the term on wikipedia. This may speed up your search a little.