Can you please go through the How do I restore my tabs from last time? article and see if it helps you? Thanks!

--Tobbi

EDIT: Sorry, I meant this: Restore previous session - Configure when Firefox shows your most recent tabs and windows

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

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

To see all History and Cookie settings, choose:

• Tools > Options > Privacy, choose the setting Firefox will: Use custom settings for history
• Deselect: [ ] "Always use private browsing mode"

Do not use "Clear history when Firefox closes" to clear the "Browsing History".

• Tools > Options > Privacy: 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.

Sorry guys, those don't seem to be helping. It looks like Firefox isn't even saving my changes when I click "OK". If I go back and check the settings, or open a new page, it's back to what the old settings were (in the case of Tools > Options > Privacy, it stays as "Firefox will: Remember History"). Any thoughts? :/

then see How to fix preferences that won't save

http://kb.mozillazine.org/Preferences_not_saved

thank you

That is probably OK.
If all History settings are default then the custom settings are hidden and you see "Firefox will: (Never) Remember History".

The "Use custom settings for history" setting allows to see the current history and cookie settings, but selecting that setting doesn't make any changes to history and cookie settings. Firefox shows the "Use custom settings for history" setting as an indication that at least one of the history and cookie settings is not the default to make you aware that changes were made.

Thanks, ideato! It was a corrupt prefs.js file. Thanks you also, cor-el, for the help! :)

You are welcome.