Customize Your Site won't load (in any browsers, all diagnostics performed)

Hi!

I’ve recently installed WordPress on localhost on my Mac (there was me thinking the hard part was over!). After logging in, I clicked the Customize Your Site link only to find that nothing will load. This is the case in Safari, Firefox and Chrome.

Don’t worry, instead of coming straight here crying for help, I’ve read the Master List and performed all the diagnostic steps suggested before posting. Thus, I have:

1. Checked that the problem persists in all browsers, as already stated;
2. Flushed all caches and cookies;
3. Enabled SCRIPT_DEBUG (should I disable this now, by the way?);
4. Performed the suggested diagnostic steps using the error consoles on all three of the aforementioned browsers.

Below are the error codes that were generated from each browser:

Safari: [Error] Failed to load resource: the server responded with a status of 412 (Precondition Failed) (localhost, line 0)

Firefox: downloadable font: rejected by sanitizer (font-family: "dashicons" style:normal weight:normal stretch:normal src index:0) source: https://localhost/wp-includes/fonts/dashicons.eot

Chrome: GET https://fonts.googleapis.com/css?family=Open+Sans%3A300italic%2C400italic%2C600italic%2C300%2C400%2C600&subset=latin%2Clatin-ext&ver=4.3.1 net::ERR_PROXY_CONNECTION_FAILED

I can provide screenshots of this error messages if necessary.

I’ve tried to follow all suggestions before posting, but I am brand new to WordPress and am completely stumped, so I apologise if I’ve missed anything obvious or have broken some sort of protocol. In any case, any advice is very much appreciated! ??