Additionally I had many pinned tabs. Is there any way to get these back?

Going back : unfortunately 56.0.2 and below is no longer safe to use for every day use do to secuity issues, but 52.5.0 ESR is. It will continue to get security updates until May 2018, and you can download and install it from this page: https://www.mozilla.org/en-US/firefox/organizations/all/ Note : Legacy Extensions will be deleted or removed in any version update after May 2018.

You should make a backup of your Profile before going back and just because: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Please let us know if this solved your issue or if need further assistance.

Thanks, this is exactly what I ended up doing in order to recover my lost tabs. The real problem remains, however, that Quantum failed to restore the closed session. As long as that issue persists, Quantum lacks a critical feature and the reliability of its predecessor.

I would like to use Quantum, and will obviously be forced to upgrade in future, so I hope that this issue will be fixed soon.

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar to ensure all open windows are closed, otherwise only the last closed window will be restored.

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox
• Linux: File -> Quit

Thank you for your input, but that is not the issue. This is something that Firefox Quantum developers will need to investigate.

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

I do not have it set to clear history. I am not sure that you have understood the issue, as outlined. At any rate, Quantum was set up with the same settings as the previous generation of Firefox, and it worked perfectly before Quantum, even when multiple windows with multiple tabs had been closed, because it was that good at remembering previous sessions. The fact that Quantum has failed to do this is a complete surprise, and the reason I am hoping that Quantum developers will investigate.