The first thing to check is 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

By default, you should be able to recover up to 3 closed windows.

And I know what you mean about closing a window before you realize the consequences. Firefox doesn't have a method to prevent your older session from being replaced in that scenario, so I turned on the first checkbox on the Settings page to protect myself from that situation:

Startup [x] "Open previous windows and tabs"

There are some session-related add-ons you could consider as a further backup. These keep track of the current page in the open tabs, but do not store the full back-forward history of those tabs. I haven't tested any of these in the last year, but as a starting point:

Use database storage:

• https://addons.mozilla.org/firefox/addon/tab-session-manager/
• https://addons.mozilla.org/firefox/addon/session-boss/

Use bookmark storage:

• https://addons.mozilla.org/firefox/addon/session-sync/
• https://addons.mozilla.org/firefox/addon/my-sessions/

Bookmark storage is more robust in that Firefox backs it up regularly. However, having the extra data show up when you are searching your bookmarks may be annoying.

You can try to restore a recent upgrade.jsonlz4-<build_id> when available or use a utility to browse Windows System Restore points to see if you can find a recent sessionstore.jsonlz4 file.

You can look at this tool to inspect a compressed jsonlz4 sessionstore file.

• https://www.jeffersonscher.com/res/scrounger.html

You can copy a file from the sessionstore-backups folder to the main profile and rename the file to sessionstore.jsonlz4 to replace the current file with Firefox closed.

• make sure to backup the current sessionstore.jsonlz4

The first thing to check is 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

I have that option enable. I'll try the extentions you suggest to me. I hope it could help little bit. Also, here the common scenario where I loose my the tabs. Google Drive. Sometimes, the recent ly closed windows/tabs are greyout.

You can try to restore a recent upgrade.jsonlz4-<build_id> when available or use a utility to browse Windows System Restore points to see if you can find a recent sessionstore.jsonlz4 file.

I did, but sometimes the tabs was too old and I already delete/add a lot of tabs. Well, not all the tabs was importany, but when its gone, it just soo annoying.