I've been using Amazon's great ElasticFox browser plugin for managing my Amazon EC2 instances. I've often had the need to manage 200 or so virtual machines, and the standard web-based dashboard is both glacially slow and prone to crash my browser.
One problem is that ElasticFox which was last updated sometime in September 2010, is "not compatible" with Firefox 4.01. There is an extremely simple fix for this:
Open the XPI file (it's just a standard ZIP file), edit the install.rdf file (an XML text file) and replace the maxVersion from 4.0 to 5.0 - this allows it to install on Firefox 4.01.
And.. that's all there is to it.