Installed it from the website, logged-in with my Firefox account and got redirected to allizom.org ("Mozilla" spelled backwards!) which has an untrusted certificate. Not a great first experience :(
I'm on 59.0.1 (64-bit) for Ubuntu Artful (from the official repos). This is quite an odd bug, thanks for the link (and the link from the sibling comment). I'll keep an eye on the bug reports :)