[varikin]

But firefox doesn't seem to be in the list, though I am using the Firefox Nightly so that has something to do with it. I have Adium (lot of sparkle update checks), Chrome (just used for testing), iChat and a couple other random one-offs.

[0x0]

Firefox seems to be "blacklisted" by Apple, see /System/Library/CoreServices/CoreTypes.bundle/Contents/Resources/Exceptions.plist :

                <key>org.mozilla.firefox</key>
                <dict>
                        <key>LSFileQuarantineEnabled</key>
                        <true/>

[mcpherrinm]

Nightly is org.mozilla.nightly, so that explains the grandparent's behaviour differing, since the Apple blacklist does not include it.