I have exactly the same problem than randy.bennett :
"For some reason, the AddThis toolbar now only shows this: "Share Page: Menu Unpopulated" on the left and a search window on the right. When I check AddThis under Tools, it still shows that I have all the services mentioned above selected, but they are not showing up in the toolbar.
I uninstalled and reinstalled AddThis but still didn't work. Checked the Firefox AddOns feature and it has AddThis installed."
I have started again Firefox, but it's always the same problem : no one icon of AddThis is showing in the toolbar.
Thank's you for your help.