Tools > Options > Privacy > Location Bar: When using the location bar, suggest: Nothing

See Smart Location Bar

That does NOT work. Why does everyone keep posting this as a solution to the "autocomplete" problem? Once you change it to suggest "Nothing" it just goes back to the way it was once you close the browser and open it again. Why does Firefox have to make something that SHOULD BE so simple to fix, so freaking complicated!? So if anyone knows REAL solution to this problem, please tell me!

If a setting doesn't stay after closing and reopening Firefox then you have a problem with saving preferences.

See http://kb.mozillazine.org/Preferences_not_saved

Such an issue can also be caused by an extension.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems