How to save Unity preferences?

On one Mac, whenever I change the Unity Preferences [Command + ,], they’ll successfully be saved, and my colours and other settings are restored the next time I load up Unity.

On another (this one), no matter what I change, each time I load up Unity, the preferences default to their default settings and have forgotten everything I’ve setup.

Why is this, and how do I fix it?

// btw, I have already checked the Preferences folder in the ~/Library/ folder of the Mac not saving, and preferences are all set to read/write for the files in there.

This might be because my firewall is blocking Unity’s access to the net. However… why should that be an issue for saving local preferences?