Hello,
Sadly, storage breakage is a Firefox issue. Addons these days can't access drive or database directly, they only instruct browser to store or load data. If thumbnails are missing, it's likely result of a broken IndexedDB database.
More info:
https://github.com/fastaddons/GroupSpeedDial/wiki/Fixing-broken-dials-page

Regarding the Pro version, well it's to cover the development cost. Since I'm not payed by Mozilla, I have to earn money somehow, and most of my addons are free, so this one is the only one that actually keeps me and my work alive :).
It's a pretty bad paying job being an addon developer, that's for sure :(.

Best Regards,
Juraj Mäsiar

Hello,
Only these features are payed:
https://github.com/fastaddons/GroupSpeedDial/wiki/PRO-version-features
Everything else is free, which should be a huge majority :)
Best Regards,
Juraj Mäsiar

Hello,
I'll fix the broken popup search in the upcoming release.
If there is more issues with the last release, please let me know! I'm working on several issues now and I plan to release it in upcoming days.
Best Regards,
Juraj Mäsiar