Hello,
There are multiple recovery options available, see this article:
https://github.com/fastaddons/GroupSpeedDial/wiki/Recovery-of-your-dials,-how-are-dials-stored-and-how-to-make-a-backup

Also, it's unlikely that browser just deleted your addon data - even if you used Firefox Reset, you will have a backup on your desktop.
Best regards,
Juraj Mäsiar