Works for me too. Bruce, could you start Firefox via the Terminal (/Applications/Firefox.app/Contents/MacOS/firefox) with the extensions.zotero.debug.log pref enabled via about:config and send support@zo.....org the output after loading that page? Thanks.
Looks like this was a problem in 1.0.0b4.r5 that Simon has since fixed in the dev branch. It's in the main code rather than the translator, so we can't fix it via the repo. Should be fixed with the next release.
When do you expect the next update? Should I move to the dev xpi?