Safari not loading Gmail; Google/YouTube invalid certificate

I've tried changing DNS servers to OpenDNS's, I've cleared my history and website data from Safari, and I've uninstalled all extensions… but the browser just won't load Gmail! Whether I click on Sign In at google.com or enter gmail.com in my address bar, the page just never loads.

Not sure if related, but when I try visiting YouTube, Safari says the certificate is invalid. I click to proceed anyway, and the page automatically redirects to http://ift.tt/1xu3wEW? It's a blank page. What's up with the auto-redirection? When I try to visit youtube.com again, I get served a site with no stylesheet or images. google.com loads without a problem although Safari throws up the invalid certificate warning as well.

Gmail loads fine on the Safari-only guest account, if it helps. My hosts file is ok. I'm using OS X 10.10.1 and Safari 8.0.2.