MacOS – Safari searches in the title bar require tapping “return” twice

You can use the Detox extension for Safari and Chrome, which fixes this on Google and Twitter.

This happens because Google switched to a client-side redirect for their tracking links (in JavaScript, I think) so the browser thinks the tracking page is the page you wanted. I'm not sure why. Twitter does the same thing, but it's so that they can grab the referer when you click on a t.co link from a client or another website.

You can use Karabiner with a private.xml such as this:

<?xml version="1.0"?>
<root>
  <appdef>
    <appname>SAFARI</appname>
    <equal>com.apple.Safari</equal>
  </appdef>
  <item>
    <name>Swap ⌥↩︎ and ⌘↩︎</name>
    <identifier>SwapAltEnterAndCmdEnter</identifier>
    <only>SAFARI</only>
    <autogen>
      __KeyToKey__
      KeyCode::RETURN, VK_COMMAND | ModifierFlag::NONE,
      KeyCode::RETURN, ModifierFlag::OPTION_L
    </autogen>
    <autogen>
      __KeyToKey__
      KeyCode::RETURN, VK_OPTION | ModifierFlag::NONE,
      KeyCode::RETURN, ModifierFlag::COMMAND_L
    </autogen>
  </item>
</root>

You can find the manual here to know how to edit the private.xml file and update your configuration.

You have to check the small checkbox of the newly defined rule to make it work.