Sorry to hear about this problem. Could you start off by backing up the session files you have right now? Here's how:

You can open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter/Return

In the first table on the page, click the "Show in Finder" button (on Windows, "Open Folder" to show in Windows Explorer).

In your profile folder, scroll down and double-click into the sessionstore-backups folder. Save all files here to a safe location, such as your Desktop or Documents folder. If not too much time has passed, we may be able to use them to recover your lost tabs.

The kinds of files you may find among your sessionstore files are:

• recovery.js: the windows and tabs in your currently live Firefox session (or, if Firefox crashed at the last shutdown and is still closed, your last session)
• recovery.bak: a backup copy of recovery.js
• previous.js: the windows and tabs in your last Firefox session
• upgrade.js-build_id: the windows and tabs in the Firefox session that was live at the time of your last update

Could you take a look at what you have and the date/time of the various files to see whether you think any of them would have the missing tabs?

(Windows Users: By default, Windows hides the .js extension. To ensure that you are looking at the files I mentioned, you may want to turn off that feature. This article has the steps: https://www.bleepingcomputer.com/tutorials/how-to-show-file-extensions-in-windows/.)

To view the contents of a session history file, you can drag and drop it onto this tool: https://www.jeffersonscher.com/res/scrounger.html (that's on my website, so if it doesn't work, let me know).

Hi thank you, that's definitely helpful. The last upgrade was on 9/7, so I'm able to retrieve some but not all of the tabs. Still, very helpful.

2 things - - is that the most recent that I can retrieve? - also. I realized that this didn't happen (I don't think) while upgrading, but rather while adding a new add-on.

thoughts? thanks again.

deggy said

- is that the most recent that I can retrieve?

Do you have a backup regime in place, for example, using the "Time Machine" feature? That may provide access to a more recent session history file, either recovery.js, recovery.bak, previous.js or, at the main level of the profile folder, sessionstore.js (only exists after a normal shutdown).

- also. I realized that this didn't happen (I don't think) while upgrading, but rather while adding a new add-on.

Yes, after losing my session one too many times after forgetting that some program started Firefox to display a page and closing that page would close Firefox, I switched my startup setting to always restore the previous session. That's slower, but safer. See: Startup, home page, tabs, and download settings.

You can set the on_demand prefs to true on the about:config page to make Firefox start as quickly as possible (I use mozilla.cfg to do this for all profiles and Firefox versions). I have quite a few tabs pinned (28) to have them available for easy access and pinned tabs are restored by default.

This also helps in case of a restart (e.g. crash or memory issues) or if you accidentally close Firefox.