Rated 4 out of 5 stars

Nice Speed Dial Extension.
Really like that is syncs with all my bookmarks (my current Fast dial extension uses different mechanism for that).
It would be nice to see ability to add custom images for the tiles (actually its a deal-braker for me).

At the same time I've run into some nasty bugs.
Default tile thumbnail mechanism kinda buggy. Looks like it makes a previews before initial site finishes loading. Because of that for YouTube I always get a blank white thumbnail, for SoundCloud - same blank image with site header only.
I tried to use "Capture in new tab" feature instead but the result isn't that smooth either.
Images look vertically stretched (most noticeable by looking at circles that became ellipses).

Lastly there is no scroll-bar even if page is scrollable (when adding many tabs) Using FF58 on Win10x64.

All in all I do like this addon and would like to use it but current issues prevent me from migrating to it completely.

This review is for a previous version of the add-on (0.0.1). 

Custom images will be available soon (for websites, folder and back icon).

For thumbnails, the iframe method is the most transparent but some web site use inline script and I can not render it correctly. I'll provide an alternative method with a web service but I prefer a local solution.
Regarding the capture in a new tab, it takes the current browser window ratio. I'll work on it for the next release.

And for the scroll-bar, it's not a priority but perhaps in the future.