There was a thread on this a few weeks ago. It's a little hard to follow, but I think cor-el's suggested settings changes hid the icon bar once all was said and done: HOW TO REMOVE NAVIGATION BUTTONS AND ICONS FROM HOME SCREEN IN FF13.

(There might be other threads with alternate solutions, but this is the one I remembered.)

Here's an alternate approach using the Stylish add-on.

(1) Install Stylish and restart Firefox.

https://addons.mozilla.org/en-US/firefox/addon/stylish/

(2) Open the home page in a new tab.

(3) Look for the "S" icon on the Add-ons bar (press Ctrl+/ to display the bar if necessary). Click the icon and choose Write new style > For this URL... Stylish should display a dialog with this rule text:

@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document url("about:home") {

}

(4) Copy the following and paste it into the new rule on the blank line between the curly braces, then click Preview to confirm that it hides the bar on the home page.

  #launcher{display:none !important;}

(5) Assuming it worked, go ahead and give your rule a name, such as No Homepage Launcher

Stylish has many other uses, since it can modify not just web pages but also Firefox's "chrome" (toolbars, menus, etc.).