You need to contact the addon developer to update their addon so it can work with the latest version.

Sometimes Firefox may detect a problem during an upgrade and "Reset". In that case, a folder named Old Firefox Data should appear on your desktop, and you would have to reinstall your extensions and recustomize your toolbar.

If that happened to you, can you find the Old Firefox Data folder? If your speed dial sites are stored locally (not in the cloud), the list probably is in that folder. However, I'm not sure how best to recover that into your current installation of Firefox. It might be that the extension author can help with that. He posted his email address on the right side of the page where it says "Support E-mail".