If MySpeed for Mac suddenly stopped work with Safari, it's most likely that your Safari just installed an update.

When MySpeed is installed there are certain Safari Sandbox settings that are adjusted to allow MySpeed to work with Safari and when Safari does an update these settings revert back to the original settings before MySpeed. Re-installing will correct the issue even if you're installing the same version that you already have.

Download and install this latest update, depending on your license: 

MySpeed for Mac 5.2 (1312) or later, click here.

MySpeed for Mac 6.2 (6323) or later, click here.

Applies to: MySpeed for Mac Version 5 and 6

Operating System: OS X 10.7+

Browser: Safari 6+