This is a shockingly common problem for people. I can tell they feel uncomfortable just typing without a place "where" the typing will go. Many people will click the magnifying glass and then again place the cursor into the search field. Same with google, they will click the search field, then the cursor moves to the address bar, they feel surprise, and then place the cursor in the address bar a second time.
Alt+Left arrow makes _loads_ more sense than "Backspace, but conditionally, only when not engaged in a text entry field."
I'm sure it's a mess for less tech savvy people trying to do searches on companies that have .com or .net suffixes on their names.
I change my Firefox copies to have separate boxes, and no search from url bar. I don’t recall offhand as it’s muscle memory, and I’m on a phone, but I think it’s ctrl-k for location and ctrl-l for search.
He also refuses to learn shortcut keys because he never learned to touch type, and refuses to type even 1 character more than he has to, so he has a lot of common things he would type stored on a virtual clipboard that he recalls with ctrl+`, and will paste from that to avoid typing.