Just found a Google Page rank extension for Firefox. It's an easy extension to install - just click the link to install in a Firefox browser. You might have to tell Firefox that it's okay to allow this to be installed (security feature which you'd rather have than didn't)

With the advent of (Tiger's) Dashboard widgets, I've chosen not to install Konfabulator and the Page Rank Widget... I figured that one set of Widgets is enough for anyone... plus the floating panel was either always hidden behind browser windows or on top getting in the way!

Read more about Google Page Rank. Stephen Powell refers to it as a measure of Google Juice...