2 ways for browser to do kanji look-up

Thanks to S.C. for the first mention:

Google Chrome is an alternative browser (others are Firefox, Internet Explorer, Opera, Safari, and so on) known for it's speed and security as well as "extensibility" - it supports apps, extensions (in browser functions), themes, and a webstore for finding these tools.
     Furigana Injector from Akira Kurogane is an extension to Chrome that (on a click) looks up the readings for kanji words and inserts them inline as furigana.
It also provides quick dictionary lookup (mousable), supports kanji levels (based on "most common kanji" count.
     You can find Google Chrome at http://google.com/chrome
Once you install Chrome, you can add the extension by visiting the Google Chrome Web Store
 - search for "furigana";
 - look under the extensions tab
 - install Furigana Injector from (Akira Kurogane)
 - the Injector waits for a Japanese Language page before "volunteering" to help 

And thanks to S.T. at Asia Pacific World for reply with even better alternative:

There is another plugin with similar functionality called rikaichan. I have used it for several years, and rather prefer it to Furigana Injector. Rikaichan was created for Firefox, but now there is a version for Chrome called Rikaikun.

After using Furigana Injector for just a few minutes, it is easy to see that rikaichan is substantially smoother and less glitchy. And even within the first few words of Furigana Injector's "welcome page", you can see an advantage of rikaichan / rikaikun. In the sample Japanese text there, Furigana Injector separates 医学生 into 医学 and 生, providing a separate pop-up translation for each part, whereas rikaichan / rikaikun recognizes the whole thing as one word, and translates it as a whole.