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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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wrote, on December 7th, 2006
Thanks, its very useful.
wrote, on December 7th, 2006
you have GOT to post some extensions/plug-ins that are NOT for Firefox !
All of us dont like FF you see
Opera rules for me !
wrote, on December 7th, 2006
Mr.Cool: Yeah, but unfortunately Opera doesn’t support Extensions and Widgets sucks a lot
(Nothing offensive)
wrote, on December 7th, 2006
haha ! None taken.
And btw, yes, thats the only sad point about Opera. Its not VERY customizable like FF. Hope they do something in that department cause i can’t think of going back to FF now ! (praise the Opera Wand
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wrote, on December 14th, 2006
[...] Honestly, I am not a great fan of Google Toolbar. Last time when I installed it, my browser crashed every now and then. Majority of us use Google Toolbar just for the sake of Spell Checking or viewing Pagerank. Firefox 2 comes with a native Spell Checker and SearchStatus Extension shows pagerank in an unobtrusive manner. [...]
wrote, on April 28th, 2007
I know this is a quite old post, but i must update crash status, it crashes when your regional settings differ from gg toolbar language. I’m also using this extension and its very useful for alexa and google rank previewing.
wrote, on November 15th, 2007
This extension also shows the info faster that the google toolbar. It has become a very useful tool for me and I am sure its popularity would grow
wrote, on August 10th, 2008
Love this tool, great for finding “Dofollow” forums!