Install one of the following: https://addons.mozilla.org/en-US/firefox/addon/2221 https://addons.mozilla.org/en-US/firefox/addon/777

Its simple, no addons at all. Type about:config in the adress bar and seach for browser.newtab.url and you will find the string you need. Change it to the page you want to open as the newtab. and thats it.

To My last reply: I found out that this sting dose not always exsist, if you have not yet updated then its a good idea. A link on how to update: https://support.mozilla.org/en-US/kb/Updating%20Firefox#Manually_check_for_updates

Is there a config setting that would tell Firefox to open my new tab url with the cursor on the web page and not in the Firefox location bar?

For example, I've entered www.google.com as my new tab url, and new tabs now open to google. But I can't start typing right away as the cursor is in the url field and not on the google page.

No. If you change the setting of the new tab URL then the focus appears to be set to the location bar and not to the web page.
An alternative is to use the toolbar Home button or create a bookmark on the Bookmarks Toolbar and middle-click that button to open the link in a new tab.