When you load a previous session, the History menu may show a "Restore Closed Windows" section or "Recently Closed Windows" sub-menu. Can you use that to get to your missing tabs?

I looked under all the ways to bring up precious tabs, including under History, but it was too late. All the tabs disappeared. Just by me pressing on something wrong. A million times before, I pressed the Restore button, and both windows with the groups of tabs would pop up. But this time, I must have done something funny. But opening a new tab next to the Restore tab, it made my previous pages disappear.

You can store collections of tabs by bookmarking them. Open them again by going to the bottom of the list in the folder and choosing "Open All in Tabs". Bookmarks are easy to back up.

For Firefox 32 and earlier:

Perhaps I should have suggested this originally:

Please back up all your sessionstore files to a safe location for potential recovery/salvage operations.

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

In the first table on the page, click the "Show Folder" button.

In the window that launches, scroll down and save a copy of all files whose names start with sessionstore to a safe location, such as your 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 in among your sessionstore files are:

• sessionstore.js: the windows and tabs in your currently live Firefox session (or, if Firefox is closed, your last session)
• sessionstore.bak: the windows and tabs in your last Firefox session
• sessionstore.bak-datetime: the windows and tabs in the Firefox session that was live at the time of your last update
• sessionstore-1.js (or other numbered files): windows and tabs saved at a time when Firefox was unable to update the sessionstore.js file

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?

Whoops, these files moved and got new names in Firefox 33... here's a new version of my previous post:

Please back up your session history files to a safe location for potential recovery/salvage operations.

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

In the first table on the page, click the "Show Folder" button.

In the window that launches, scroll down and double-click into the sessionstore-backups folder. Save all files here to a safe location, such as your 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 is 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

You might also find files Firefox created if it could not update recovery.js (but since Firefox 33 is so new, I don't know what they would be named).

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?

Note: 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: http://windows.microsoft.com/en-us/windows/show-hide-file-name-extensions