No. Starting 2-3 years you had to go through about:config to do this, such as detailed at
https://www.reddit.com/r/FirefoxCSS/comments/qqkw5x/enabling...
and
https://connect.mozilla.org/t5/discussions/custom-search-eng...
etc.
Heaven knows what they were thinking when they made this option only available by the user adding an undocumented preference!
I needed to do this on desktop linux a few months ago to use the AI-avoiding &udm=14 google tweak[0]
So the URL entry box wasn't really needed for the main purpose. It's nice to use the feature to use with things that aren't literally search engines though. Or to tweak the URL. I wonder, is the AI avoidance thing very effective? Not that I use Google directly but still.. (I use SearXNG as meta search)
Yes, it's just a way of going directly to google's "web" search instead of "all" so you don't get the AI summary and half a screen of assorted guff before the search results themselves. In that sense it's 100% effective.
If only!