I was surprised this wasn’t a default behavior anymore. Getting Firefox 4 to save on exit wasn’t in the options either which was odd. This is how you get it back:
- Type about:config into the location bar and press enter
- Just accept the warning message and you’ll see a huge list of options. Don’t get scared of this.
- Type the following into the filter box and make sure each one is set to true. Right click and select “toggle” if it’s false.