The Alexa toolbar for Firefox is now available as Alexa Sparky - though they call it a toolbar, it's more like a status bar.
Alexa Sparky adds visual traffic graphs to the status bar of the browser which shows the site's popularity over time (based on Alexa traffic) and the Alexa rank number. [see screenshot below]
A Related Links option is added to the Firefox menu bars that shows the 10 websites related to the web page that's currently open in your Firefox browser.
Right click the traffic graph in the status bar to quickly access the Alexa Detail pages, Cached Pages, Search Pages and more.Download Alexa Toolbar for Firefox at www.alexa.com. Not sure if this is compatible with the latest release of Firefox 18.104.22.168. Thanks Eklavya.