Hello,
You can customize the group layout in the "Edit group" window - right click group name or open main menu and click "Edit group".
More info about layouts:
https://github.com/fastaddons/GroupSpeedDial/wiki/Group-layouts
See also introduction video for more tips:
https://www.youtube.com/watch?v=mgAJTjrcIRI
Best Regards,
Juraj Mäsiar

Hello,
Group Speed Dial version 26.0 is still compatible with Firefox ESR 115, you can install it from here:
https://addons.mozilla.org/firefox/addon/groupspeeddial/versions/
(click the "[Download file](https://addons.mozilla.org/firefox/downloads/file/4348052/groupspeeddial-26.0.xpi)" below the change log)

Sadly, I can no longer bring back support in the current version of my addon due to missing JavaScript features in Firefox ESR 115. Even the newer ESR 128 is getting too old and in a few months will be replaced with Firefox ESR 140.

But the version 26.0 should work fine.

Best Regards,
Juraj Mäsiar