It's not just browsers. eg;

  $ host -v ai
  Trying "ai.home.example.com"
  Trying "ai"
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 29228

So if there was a host on my network named 'ai', http://ai would resolve there (The terminating dot being standard to indicate a fqdn, rather than a browser trick). This has been understood for a long time; rfc1049 gives us:

  Relative names are either taken relative to a well known origin, or to a
  list of domains used as a search list.  Relative names appear mostly at
  the user interface, where their interpretation varies from implementation to implementation[.]

I stress that last clause; dotless domains have no defined behaviour. "http://google/" may refer to google.example.com. (relative to my search list), google.com. (relative to a well-known origin), or google. (a fqdn). That's not browsers, or omnibars, it's been the vagueness of undotted-domains since the start.

There should be no A-labels on bare gTLDs, so "https://google" should never make sense (per SSAC053 report - https://www.icann.org/groups/ssac/documents)