I have been using Fast Dial for a while now, and over the last couple of weeks I have found that when I go into Firefox, my Fastdial previews have all been shuffled around. I also find that sometime, some of the previews are missing altogether (just a white box showing). If I log out of Firefox and back in, they come back, but in a different place.

Thanks for your reporting your experience of cells moving around in Fast Dial 2.11

Have you I wonder tried disabling your other extensions to see if what is happening might be caused by an extension conflict.

Perhaps you would be interested by Fast Dial Version 2.14
This can be downloaded here