PolarCloud.com created Rikaichan, a plug-in for Mozilla Firefox, which makes reading Japanese websites quick and easy.  In Firefox, install the Main Extension, the Japanese-English dictionary, and–if you want to–the Names dictionary.  (Restart Firefox between each of the installations).  Once you are on a Japanese webpage, right click and select “Rikaichan” to enable it for that tab.  Every page you visit in that tab will have Rikaichan enabled.  Then, simply roll over any kanji with your mouse to see readings, English definitions, compounds, etc.