The only replacement I could find for the lagacy Desktop add-on.
Missing features / Bug:
* I miss the possibility to create multiple speed-dials or sub-dials. Please consider adding this feature! Interestingly the "Add to Speed dial" option appears on the Speed dial itself, so in theory you could create sub dials.
* the speed-dial screenshots are always in a fixed grid and cannot be freely placed.
* The size of the browser window affects the aspect ratio of the screenshots causing various heights. Examples of this can be reproduced when you Add to Speeddial with an active side panel or when resizing the browser screen.
* Speed dial won't work in a second window you open in Firefox.
* Speed dial will show unexpected behaviour when you have a custom home screen URL set.

For the rest it seems OK. I hope it will proof to be as stable as Desktop, surviving several upgrades until FF stopped supporting legacy add-ons.