So far so good. There are lots of options and at this moment have no time check all of them. Good job.
Update - Oh yes Juraj you had a very good idea developing this plugin. At first I thought, well, I'll give a try thinking I already have lots of bookmarks and this might be redundant. No it is not redundant at all. In fact it is much more powerful and easy to maintain and use than the native Bookmarks.
Thanks again.

New Update:
I dropped one star cause things are complicating. Maybe there are too many options or the whole thing is getting crowded and confused. Caveat emptor Juraj. A cute baby may be turn a monster.

It's all OK. Very good.
But with the last Firefox version (70.0.1) I lost all favorite site groups and in the GSD Option I didn't find the possibility to load the old saved setting.
So I downgraded to Firefox version 70.0.0 and all is now OK.
Bye

Excellent add-on, i like that is compatible with other discotninous add-ons and the free cloud sync feature. Highlly recommended.

Everything was perfect until I updated FF several days ago, and then Speed Dial started to crash FF and itself also. Now it dont even show my bookmarks and groups, and shows an error.

Environment health-check error: Error
Could not establish connection. Receiving end does not exist.
o@moz-extension://62dfe56a-2f32-44ce-8578-8095c19094be/dial.js:1:19374

Error: Could not establish connection. Receiving end does not exist.

Environment: Group Speed Dial 14.0; info: os: win, arch: x86-64; name: Firefox, vendor: Mozilla, version: 70.0, buildID: 20191016161957;
Running time: 4712 / 22017769
Stats: NA - 12,12,11
Runtime errors:
error getting runtime errors: Error: Could not establish connection. Receiving end does not exist.
Version: 14.0; OS: {"os":"win","arch":"x86-64"}; Browser: {"name":"Firefox","vendor":"Mozilla","version":"70.0","buildID":"20191016161957"};

The Best speed dial.

I used to love this add-on until the moment I updated my Firefox to 70. Now it is a crap working full of problems. Are you trying to fix the issues?

Best speed dial we've ever tried. And we've tried them all. It does everything it promises and has no bugs as far as we can tell. It even allows animated gifs as speed dial thumbnails which we love. Fun stuff. It's the only one we use now. Very highly recommended.

I have set this as the New Tab page on my Android tablet, and it is exceptionally good with a wealth of settings for further customisation. I use groups in the same way that I use folders on the bookmarks toolbar of my Windows Desktop.

The only small point - which has been mentioned by another user, is that it could be even better if it were possible to rearrange the thumbnails within groups, but the developer's response suggests that this may not be possible. However, it is nonetheless still a superb extension.

Excellent add-on permettant l'organisation des marque-pages dans des onglets totalement paramétrables, leur synchronisation entre différentes machines et dans le cloud.
Impossible de s'en passer quand on l'a essayé.

Superb extension and the best of its kind (by far) that I have tried.

Highly customisable with loads of excellent features, and it's easy to use too.

Thanks :)

Only issue I'm having is that when refreshing the thumbnails for a couple of sites, the images are sometimes blank. This happens regardless of how long I set the delay for. It's most probably a site issue and can be resolved by 'refresh image by visiting the page +5' which is only a minor inconvenience.

One feature request would be to load thumbnails in dark mode if possible please. That would be awesome.

Edit: Wow...the new refresh method is amazing!

Thank you so much.

I will contribute when I can. You are doing an amazing job :)

drag & drop feature doesn't work in android.

I really love this addon and have used it without any problems for a long time. Thank you! There is only one problem now: Since the firefox update 69.0 some days ago, the tabs are crashing every few minutes. I disabled all Addons to see where the problem is, and it only happens when Group Speed Dial is activated. Firefox is then showing the "Sorry, this tab crashed" page. Do you have any suggestion how to solve this? Thank you and all the best