Great extension. Among many similar speed dial addons for Firefox which I have tried, this one is the best.

After some tweaks in setting this is the one that resembles the Opera speed dial the most. And can be even better because there are MANY options to make it as personalized as possible.

For people who have problem with white thumbnails and no webpage preview - this is caused by canvas fingerprinting protection in Firefox. If you want to load all thumbnails: turn off fingerprint protection in about:config and after you thumbnail load properly, turn it on again.