@bamh1d Well, I can now report that the problem somehow seems to be resolved. That is to say, I can once again open links in Opera without having to close/re-open it. I don't understand any of this - how having an active Google tab seemingly blocked opening of other links, and how the problem apparently was fixed without any intervention from me. Anyone care to comment?
Opera supports search shortcuts, and unfortunately Z is the shortcut for Amazon. you either need to type a G before the whole thing (to force Google) or put it in quotes to force it to be considered a single search term.