Hmm, that's not normal. Let's start by checking Firefox settings. Could you make sure you do not have Firefox set to clear browsing history when it closes:

Settings page > Privacy & Security panel > History section

With the selector set to "Firefox will: Use custom settings for history" you can see whether there is a checkmark in either of these boxes:

• "Always use private browsing mode" - this is incompatible with restoring your previous session at startup
• "Clear history when Firefox closes" - If there is a checkmark, click the Settings button to the right to review the categories of data set to be cleared. If Browsing & Download history is selected, un-check that box.

If those settings are normal, could you check whether Firefox is saving your session history as you browse? To do that, open your profile directory (Profiles - Where Firefox stores your bookmarks, passwords and other user data) and double-click into the sessionstore-backups directory. The recovery.jsonlz4 file should be updated as often as every 15 seconds if you have opened or closed a new page/tab/window. Can you tell whether that is happening in real time?

And just in case:

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
• (menu bar) History > Recently Closed Windows

Can you recovery anything there?