I'm assuming that the problem is the autofill fuction within in the address bar itself, because you can just ignore the suggestions that appear in the autocomplete drop-down below the bar.

Assuming that's right, you can turn off that feature using a hidden setting. Here's how:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the search box that appears above the list, type or paste urlb and pause while the list is filtered

(3) Double-click the browser.urlbar.autoFill preference to switch it from true to false.

Does that help?

The error was mine, and it was the result of using firefox sync and reinstalling my laptop with a similar configuration... but a different computer name. Firefox sync updated my tabs on my desktop system, but because the system name was familiar, I did't twig to what had happened. I have corrected the situation by unchecking sync tabs. Sorry for raising the issue. This was not a firefox problem. And thanks for the attempt to help. A sharper Sunday brain was all that was required.