Sorry, but I suggest you download Firefox from Mozilla and us sync to get the data over. This way if something goes boom, you have it in another browser. see screenshot https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

I run several versions of Firefox plus Waterfox on my laptops with no issues. Just download, unzip, and run firefox-bin from the folder.

What OS? X11 or Wayland?

To restore last session manually, see details here --> https://support.mozilla.org/en-US/questions/1420979#answer-1597405

Hopefully these links will help.

https://support.mozilla.org/en-US/kb/how-restore-browsing-session-backup https://support.mozilla.org/en-US/kb/restore-previous-session https://support.mozilla.org/en-US/questions/1409242#answer-1572631

I have experienced the issue two or three times (not recently) but I have all open tabs bookmarked.

None of those suggestions helped.

OS: Ubuntu 20.04LTS

This may shed some light.

https://support.mozilla.org/en-US/kb/restore-previous-session#w_troubleshooting

If you have a lot of open tabs, changing the value of this preference in about:config may help. It relates to the History option Recently Closed Tabs. browser.sessionstore.max_tabs_undo

https://support.mozilla.org/en-US/kb/about-config-editor-firefox

That hasn't helped either.

In case you use "Clear history when Firefox closes".

• do not clear the "Browsing history"

• Settings -> 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

See also:

• https://support.mozilla.org/en-US/kb/restore-previous-session

It's set to remember history.

In History, restore previous session is greyed out.

What's set here? see screenshot

I have it set to remember history.

My session failed on Nightly today, restored it, but this is happening a wee bit to often.  ;-/

Session restore continues to be stable and reliable for me on Nightly.

I went to open gmail and it restored all my tabs

This could happen if you have separate installations and/or profiles on your system.

Search your apps for "firefox" and see how many items show up. You can change the default in Ubuntu Settings > Default Apps > Web.

Go to about:profiles in the address bar to see other profiles. You won't see profiles across different package types (snap/flatpak/apt).

Search your apps for "firefox" and see how many items show up. You can change the default in Ubuntu Settings > Default Apps > Web.

Showed only one profile

Go to about:profiles in the address bar to see other profiles. You won't see profiles across different package types (snap/flatpak/apt).

Showed two profiles so I deleted the non default one.

Hi

Thank you for your question. This is something that we are currently looking into and hope to be able to respond to you soon with a more complete answer.

Are you using the startup setting to restore the previous session automatically or do you use "History -> Restore Previous Session" ? You may have to check "History -> Recently Closed Windows/Tabs". This might be best:

• Settings -> General -> Startup -> Open previous windows and tabs

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox Title bar, especially if you have multiple windows or Private Browsing windows open to prevent losing tabs in unnoticed windows.

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