Update: Just got a note from Patrick. Looks like this is fixed, and the voting form is now working in both Safari and Firefox. See his note here: http://rhizome.org/editorial/fp/blog.php/632#51910
I also observed that the voting form does not appear in Safari 3.1, but now I see it also not showing in Firefox. I wonder if the form simply does not load if the proposal already has a certain number of votes? This would fit with encouraging around the same number of votes for each proposal.