Hello,
Try these steps:
https://github.com/fastaddons/GroupSpeedDial/wiki/Fixing-broken-dials-page
That could help, although it's hard to tell.
Firefox is having some issues since Firefox 149 with their database engine, I've reported it here:
https://bugzilla.mozilla.org/show_bug.cgi?id=2044020
But it's hard to say if it's related.
Can you remember if you recently made some changed to your dials? Maybe adding some custom thumbnails from high resolution images?
Feel free to contact me here: admin@fastaddons.com

Best Regards,
Juraj Mäsiar