I upgraded to 2.9 this morning and FD is now broken. After the upgrade and the Firefox restart my thumbnails loaded as tiny dots in the middle of the page. When I clicked on them nothing happened.
I uninstalled, reinstalled and I got my thumbnails back. After the reinstall I could click on a thumbnail and go to the associated link. However when I would click on the home page button and FD would reload my thumbnails were back to being tiny dots and didn't do anything when I clicked on them.