1) Set up 10 directories on your hard drive.
2) Do 10 separate installations of Firefox Portable, one in each directory. You can have all 10 be the same release number or get legacy copies of the software so they're different versions.
3) Set different user agents for each installation.
4) Make sure the .ini files for each allow for running multiple instances of Firefox.
5) Set up a different proxy for each installation.