Apple application error
This error will appear sometimes when you launch software that has been downloaded: "[Program] is an application which was downloaded from the Internet. Are you sure you want to open it?"
It is caused by extended attributes on the application and it can happen on many programs, including Firefox and Thunderbird. Here's how to fix it:
1. open terminal
2. su to admin
3. cd /Applications
4. xattr -d com.apple.quarantine Thunderbird.app
5. repeat for other applications that have extended attribs
You can check which apps contain these attribs by doing an ls -lsa. You'll see "@" on the far right of the file's permissions listing. Additionally, you can check the attribs on each file by doing a xattr -l [file/dir].