Trouble shooting section does not seem to show, so here goes again. I have left the machine set after shutting down firefox (no hanging threads.) Changed under options, to blank (my choice), home page, or last opened--- stays at last opened even if options show my choice on closing/opening. Restarted in safe mode (both windows/firefox separately or at the same time. Disabled Norton anti-virus and changed. disabled all add-ons/plug ins and changed.

any more ideas / help?

It is possible that there is a problem with the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder.

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/Session+Restore