Q: Proxy Pac and Sierra

Does the URL for your proxy PAC script begin with `http://` or `file://`?

I have this same problem but I'm using a local proxy.pac file with a URL of the form file:///Users/.../proxy.pac.

Firefox works fine with this setting, but Safari fails to connect to any web site that requires a proxy.

I ran a local web server and switched the configuration to use an http: URL instead of a file: URL and then Safari worked, so it's not related to the content of the file but rather to the form of the URL being used.  I can't figure out how to make a file: URL work, even though it worked fine before Sierra.