https://stackoverflow.com/a/34445606
FiddlerScript uses JScript.NET, which can reference .NET assemblies, and System.Threading contains Sleep.
1. In Tools > Fiddler Options > Extensions, add the path to System.Threading.dll. On my machine, this was located at C:\Windows\Microsoft.NET\Framework\v4.0.30319.
2. In FiddlerScript, add import System.Threading;.
3. You can now add lines like Thread.Sleep(1000).
- Step 1 is not required on latest version of Fiddler