Final Draft 10 and Final Draft 9 are compatible with Yosemite. The FD10 installer is HERE and the FD9 installer / updater is HERE.
Final Draft 18.104.22.168 is also compatible with this operating system but it will not be updated if there are issues. The installer is HERE and is free to registered FD8 customers.
Final Draft 7 / 6 / 5 are not compatible with Yosemite.
If you own Final Draft 7 / 6 / 5 and you want to run Final Draft on a Yosemite computer, you will need to upgrade to FD10. This upgrade is not free. Click HERE for more information on purchasing the FD10 upgrade.