In general, as we don't use the latest OSX updates for "signing" Mocha, Yosemite is not totally green lit to run Mocha. This means Mocha's ability to run on Yosemite depends on the users' security settings (which apps you allow to run on OSX). Yosemite will initially not allow Mocha to run, it is up to the user to navigate to "Security & Privacy Settings" and choose to allow Mocha to run anyway. As of right now, Yosemite seems to run Mocha without a hitch but we have not done extensive testing on the new OS. As with early adoption of any OS, there is some risk involved and we can not guarantee that Mocha will run as expected and without any bugs or errors.