Vince
Download the last version and try again 
You got a Internet issue
Your source mirror got issues maybe, not the network issue
What's you firefox version ?
How did you install this theme, is it last version, I did not find this issue
What's your system ? MacOS ?
This theme only support linux system
You can install this https://github.com/AdamXweb/WhiteSurFirefoxThemeMacOS
Do not run it with sudo