To download earlier Versions of Fast Dial, you will need to go to the Mozilla Addons site

you will be able to download your earlier Fast Dial Version there

However you will need to go to the Old Versions page.

Your older Version will probably not be compatible with the latest Firefox because of maxversion problems ..so you may find that you have to get round that problem

nightly tester tools should help

or if you prefer you could modify the Version more permanently for yourself.
but you will need to download the xpi.(explained in link)