With Zotero 2.1b4 on Firefox 4.09b on OSX 10.6.6 any kind of file import seems completely broken. Be it .bib, .ris or MODS, when I try to import the data, nothing at all happens. No error message, no status bar, nothing. I tried all kind of resetting, still no result. The only thing that worked was going back to Firefox 3 and Zotero 2. Then the import worked fine.