This can happen if you close all open windows, but leave the Firefox application running.
You need to use Firefox > Quit to close Firefox with open windows if you want to restore them.
You can also check History > Recently Closed Tabs/Windows

Make sure that you do not run Firefox in (permanent) Private Browsing mode.

• https://support.mozilla.org/kb/Private+Browsing

• Firefox > Preferences > Privacy > Firefox will: "Use custom settings for history"
• Deselect: [ ] "Always use private browsing mode"

In case you are using "Clear history when Firefox closes":

• do not clear the Browsing History

• Firefox > Preferences > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings
• https://support.mozilla.org/kb/Clear+Recent+History

Note that clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, and passwords.

• http://kb.mozillazine.org/Session_Restore
• https://support.mozilla.org/kb/restore-previous-session

None of your possible conditions apply. I always use Quit to close. I've used the recently closed tabs and that only covers a few. I've had to search through History to restore tabs. I wasn't in Private Browsing Mode and I didn't Clear History on closing. Nice try, though. Thanks.

If you experience one or more of the following problems with Firefox 23+:

• after a crash, Firefox > History > Restore Previous Session does not restore the last session, but restores the session before that one;
• YouTube videos always start muted,

then try this:

1. In the Location bar type about:config and press <Enter>.
2. In the Search box at the top, type browser.sessionstore.
3. In the resulting grid, double-click on all lines shown in bold, to set their Status to default.
4. In particular, verify that browser.sessionstore.resume_from_crash has been set to true.

I have this same problem. EVERYTHING is set correctly. I am quitting Firefox. This is a NEW issue that started about a month or two ago. I cannot get this fixed no matter what I try to do in my Preferences. Obviously a bug with Macs. This has not been the case on my pc, but only on my Mac. Hoping Mozilla will fix this bug soon, very annoying, as I usually have about 10 tabs open, and would like them restored when I restart Firefox.

Hi hoosierquilt, I'm not sure what is happening on your system, but as a short term workaround, you might consider using a session manager that captures multiple sessions.

These popular extensions offer this feature (I haven't tried them myself):

• Session Manager: https://addons.mozilla.org/firefox/addon/session-manager/
• Tab Mix Plus: https://addons.mozilla.org/firefox/addon/tab-mix-plus/

Thanks. This is so odd. I've re-checked all my Preferences, changed them, then changed them back to the proper settings, just to see if they would "take", but nothing will allow my tabs to re-appear, if I re-launch Firefox on my Mac. So weird, so frustrating. I'll try Session Manager first, and see if that fixes the issue until Mozilla can fix this bug with the Mac.