The easiest way is to use an add-on. Please see this article: [[How to make the new Firefox look like the old Firefox]]. Classic Theme Restorer has many, many options, and while its dialog is open (you can access it from the Add-ons page, Ctrl+Shift+a, Extensions section) you usually can see the effect of different choices dynamically and find your own blend of settings. If the ones you want don't seem to be there, please post back with your follow-up questions.