Earrly this morning, I was successfully able to restore themes, both full themes and personas. However, I could not get a single extension restored.
When I do Tools > FEBE > Restore > Restore Extensions, and then I select the extensions from the backup to restore, nothing happnes; there is no feedback. Then when I open Add-ons Manager, I see this:

Transfer has begun, but it's stuck, frozen. No progress. I eventually click on the X to close them.
This is actually the first time I ever tried to restore anything, so I don't know if this is something new with version 10, or what.

