The first thing is, there isn't a built-in Add-on bar in Firefox 31, so do you have one of the extensions that creates one? For example:

• Very specific: https://addons.mozilla.org/firefox/addon/the-addon-bar/
• Many options: https://addons.mozilla.org/firefox/addon/classicthemerestorer/

To display or hide a toolbar, you can use one of these methods:

• right-click a blank area of the tab bar
• right-click the "+" button on the tab bar
• "3-bar" menu button > Customize > Show/Hide Toolbars
• (menu bar) View > Toolbars

Once the bar is displayed, you can customize normally, as described in this article: Customize Firefox controls, buttons and toolbars.

Success?

i'm using the classic theme. i think i asked the wrong question, actually. i should have asked how i get an add-on from the manager to the add-on bar. most of the add-ons that i have don't even show up on the customize page. also, i want the icons to show at the bottom of the page not at the top.

If you can't drag an icon from their current position on the Navigation Toolbar (if it shows there) or from the Customize palette to Add-on toolbar while the customize window is open and you also do not find a setting in its Options/Preferences to change its position then it is likely that it is not possible to place their icon on the Add-on Bar.

Many add-ons have screen shots or other information on their pages that explains how their user interface works. Some might use only the classic menu bar instead of a toolbar button, but without checking, it's hard to know.