SearchStatus extension counts among the most useful extensions for Firefox. It displays Google Pagerank and Alexa Score anywhere on the browser along with some basic SEO tools such as fast keyword density analyzer, keyword/nofollow highlighting, backward/related links, Alexa info and few more.
It works like an Micro Alexa + Google Toolbar. While displaying Alexa Rank it sends information such as URL and IP to Alexa Web Services, so it think it might be helpful for your Alexa Rank.
Earlier I used Google Toolbar to check pagerank, but it was too bulky, so I went looking for an alternative and I found it 
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