I manually set Fiddler as the system proxy. When I tried to use Fiddler as a proxy it looped and made repeated connections to itself opening hundreds of connections. I realized what happened is since I have the Fiddler gateway set to use the system proxy and I set the system proxy manually (rather than use 'Capture Traffic' in Fiddler) it didn't realize it was connecting to itself. This may be more of a corner case but I think if use gateway is enabled then you could check that against Fiddler and see if it's the same thing, and if it is then ignore it or warn the user.