Making ^ the homepage didn’t work. https://www.reddit.com/r/firefox/comments/gw5hfq/to_ff_devs_please_bring_back_the_drop_down/ indicates a lot of other people unhappy, too
The new update brought back the “search with Amazon.com” back to my address bar. The solution given above was no longer helpful this time. B-(
However, I did find that Tools > Options > Search > Scroll down to the bottom of the page > unselect all of the search engines. You can also delete most of them from the list. It probably won’t let you delete all of them, but you can kill most of them. > Open a new Tab & click in the address bar or put a ^ in the address bar. The advertisement for “Search using Amazon.com” should be gone.