The app looks good on the first sight, built with lots of love and details!
However it is imho overloaded.
Biggest issue: it's SLOW. A start page for a new tab that takes 7 (seven) seconds to load (for every new tab!) isn't worth it. It stops my productivity. It's called speed dial for a reason.
In addition to that, like in many other speed dials, I can't arrange my icons as I want to. It's always only possible to start top left and fill a row until I can have some icons on the second row. I would like to have freedom and have variable amount of icons per row so I can even group elements in rows - like I can place icons in a Finder window.
One more: it's good that I can group elements for the speed dial, but I haven't found a way to quickly access them, e.g. by hotkey. If I could navigate with a key to switch groups it would also increase productivity. (never rely on having to use the mouse to choose something!).
One more: The search field doesn't provide value. You can choose to use Bing instead of "StartPage" whatever search that is, and it's even not focused. So opening a new tab keeps the focus on FF URL field - which in this case is good because I can start typing for an internet search and use my preferred search engine.