Rikai is an in-browser pop-up dictionary that is incredibly useful for Japanese learners! Once the add-on is installed, almost any page you browse with Japanese text becomes much less daunting, as kanji you can't read can easily be deciphered simply by hovering over the mystery character.

Depending on what browser you use, you'll be installing Rikai-chan or Rikai-kun.

For Safari users:

http://www.macupdate.com/app/mac/50176/safarikai

For Chrome users:

https://chrome.google.com/webstore/detail/rikaikun/jipdnfibhldikgcjhfnomkfpcebammhp?hl=en

(Sometimes Rikai has trouble starting immediately on pages, in this case just toggle it off and on again by clicking the icon, then try refreshing the page.)

For Firefox users:

https://addons.mozilla.org/en-US/firefox/addon/rikaichan/

There is also Rikai-sama, an upgraded version of this software that has integrated playable pronunciation! Sadly, it seems this add-on is only avaiable for Firefox:

https://sourceforge.net/projects/rikaisama/files/

1. download with link next to "Looking for the latest version?"

2. From Firefox menu, select "File | Open File..." and select the .xpi file that was just downloaded

3. Click "Install Now"