I would like a way to block all transfers made internally by Fiddler unrelated to what is being proxied because it disrupts my tests. I am using Fiddler in test cases where I need the data to be limited to what I'm sending through Fiddler. Every time Fiddler is started it makes one or more connections to fiddler2.com. For example http://fiddler2.com/Banners/BannerVersion.txt and also there's a survey connection sometimes as well. Those requests are redirected most of the time to a cloud server. I have to use various VM images to run some of the tests and I see it a lot in the packet captures. The update check I have blocked in the registry where I set BlockUpdateCheck to True. I could ignore fiddler2.com I suppose. Regardless I don't like it there is SSL traffic I can't account for or decrypt, and even if I could it would still be noise disrupting the data I need to check.
I found a preference fiddler.banners.showdefault and fiddler.telemetry.AskPermission but I'm not sure if they relate.
On a somewhat related point consider an option to disable telemetry, refer to Fiddler Script Editor disable internet access