Sorry to hear about this problem. Could you check whether either of these are available (not hidden or grayed out):

• "3-bar" menu button > History > Restore Previous Session
• (menu bar) History > Restore Previous Session

If they are missing or grayed, check either:

• "3-bar" menu button > History > Recently Closed Windows
• "Library" toolbar button > History > Recently Closed Windows
• (menu bar) History > Recently Closed Windows

Can you get the missing tabs back from a closed window?

If not, maybe they were closed in the current window or the restored window. For each window, there's also a "Recently Closed Tabs" list.

Any progress so far?

thank you very much. I have reopened many tabs, just, I think, that might be the tabs wich I had closed myself. It's ok. They were too many. I have learned. (-;