You don't reach for cmd+t by default? I use cmd+t then down arrow then enter.
(Actually my default action in Firefox is to open a new tab from the URL bar, I use Alt to open in current tab)
What is the down arrow supposed to do to the empty URL bar, though?
Yes but the parent comment said that they can open a URL in a new tab without automatically changing focus to that tab. This can be useful when you want to check something after you are finished on the current tab. Unfortunately it does not work as described. CTRL + T, type URL, then CTRL + Shift + Tab will open a new tab and then return to the previous tab.