Finally someone developed a toolbar for Firefox. It's not an official Alexa product, but good for any Firefox user. Smart PageRank's 'Smart Toolbar' is small, simple, and powerful. It gives you quick access to powerful SEO tools. It also includes the Alexa Rank and Page Rank (trademarks of Alexa and Google respectively). The usage of this toolbar will increase the Alexa Rank of the websites you visit.
Search Status is a toolbar extension for Firefox and Mozilla that allows you to see how any and every website in the world is performing. Designed for the highly specialised needs of search engine marketers, this toolbar provides extensive search-related information about a site, all conveniently displayed in one discreet and compact toolbar.
Strange that Alexa never released an official Alexa toolbar for Firefox or Mac.