if you click on an image thumbnail theres a download button top right, theres also a download workspace button in the sidebar
Oh, I see now that I didn't explain myself clearly. I got some automatic browser update and it looked like the app lost all data.
I thought that, since I didn't delete anything, this information must be in some browser memory, but disconnected from a particular website.
It's no big deal, I lost things from that day before that I didn't download. From that point I always make backups with "Download Workspace".