see this answer:

• https://support.mozilla.org/en-US/questions/1170547#answer-994429

In case you use "Clear history when Firefox closes" or otherwise clear history.

• do not clear the Browsing History

• Options/Preferences -> Privacy & Security
  Firefox will: "Use custom settings for history":
  [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an "Allow" exception you may want to keep

Thanks for the reply,

Remember browsing history and download history, and remember search and form history are checked. Clear history when Firefox closes is not checked.

I did run CCleaner and cleared cookies, but have run many times and never lost pinned tabs.

Tried to run: https://support.mozilla.org/en-US/questions/1170547#answer-994429 but could not get the files to open : recovery.baklz4 recovery.jsonlz4

This might be a little over my head

If you want to open files from the sessionstore-backups folder then you need to use a tool like this:

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

If you want to use a sessionstore file to restore a session then you need to copy this file to the main profile folder (i.e. the same level where the sessionstore-backups folder is located) and rename the file to sessionstore.jsonlz4 to make Firefox use it. Make sure that Firefox is closed when you make these modifications.

Thank you for your help. I think this all is over my head. The pinned tabs are not that important and can be duplicated later. I might be better of by using bookmarks.