See:

• Removing the Search Helper Extension and Bing Bar

You may also need to reset some prefs on the about:config page.
You can use the Filter bar at the top of the about:config page and search for bing and reset prefs that show bold (user set) via the right-click context menu.

It's not a bar, it's a whole page

Enter about:config and search browser.newtab.url right click modify, change and ok.

select tools > options > General button > Startup section > "When firefox starts:" select from the drop down menu: "Show a blank page"

See below article for further info: How to set the home page

But my instructions are more than enough.