For all of those who have upgraded to Firefox 2.0 but can't use the Pagerank Extension anymore, someone has upgraded it to make it compatible. I use this tool religiously mainly because it allows me to see if a page isn't indexed in Google by showing a N/A on the toolbar. I've checked it with Shoemoneys Live HTTP Headers to make sure it's not transmitting anything other than the Pagerank Query also Download Here
Hmm, have you ever tried Quirk's SearchStatus extension? It displays PageRank and Alexa Rank as well. It's a pretty great little extension and it works fine with Firefox 2.