fab4fan,
Sorry you are having problems.

There be something that has gone wrong or maybe more likely you have just set it to open with a homepage instead of with the tabs from the last session.

• see Startup, home page, tabs, and download settings

Check that first then please post back again.

You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox Profile Folder that store session data.

Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox Profile Folder.

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost, so you will have to create them again (make a note or bookmark them).

• http://kb.mozillazine.org/Multiple_profile_files_created

See also:

• http://kb.mozillazine.org/Session_Restore
• https://support.mozilla.org/kb/restore-previous-session