In order to login to the BuzzWord beta from a Linux machine, you'll need to use the user-agent switcher extension, and set your user agent to something like
Mozilla/5.0 (windows; U; windows NT 5.2; en-US; rv:1.9a1) Gecko/20050821 firefox/1.5
All the buttons I pressed seemed to work fine, though obviously it's even less supported than BuzzWord is normally.
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Better way to get in via Linux
We have opened up Linux/Firefox support. Please go in to Buzzword normally at http://preview.getbuzzword.com and read the configuration instructions page carefully (install the latest beta version of Flash player, change a preference), then click on the link at the bottom.