Could you make sure your Speed Dial add-on is up-to-date? It needs to be aware of the changes in Firefox 13 and later.

Do you have a Yahoo toolbar? You might need to change its settings so that it does not take over the new tab page. (I don't have it, so I'm not sure exactly where you set that. Often there is an Options button next to the Disable and Remove buttons for an add-on here:

orange Firefox button or classic Tools menu > Add-ons > Extensions category)

Yes there is a way. I finally fig it out. You have to go into Speed Dial options & under "Automatic Load" look to see if the box for "Load in blank new tabs" is checked. That's all it took for me.

install a addon like foxtab or super start after instalation go to settings, open in new tab!