Firefox 4 saves the previous session automatically, so there is no longer need for the dialog asking if you want to save the current session.
Use "File > Exit" or "Firefox > Exit" if you want to restore multiple windows.
You can use "Firefox > History > Restore Previous Session" to get the previous session at any time.
There is also a "Restore Previous Session" button on the default about:home Home page.

Another possibility is to use:

• Firefox/Tools > Options > General > Startup: "When Firefox Starts": "Show my windows and tabs from last time"

Make sure that you do not use Delete browsing, search and download history on Firefox to clear the 'Browsing History' when you close Firefox.

• How do I restore my tabs from last time?

Ah, I found my solution through investigating your suggestions. I unwittingly had "Clear history when Firefox closes" checked under the privacy tab. Thanks for the suggestions!

that's not good enough. I just don't get it. Why have they not incorporated the "use homepage for new tabs" extension as standard??? dumb, dumb, dumb. and not the extension isn't compatible for FF 5. Thanks firefox!

@ markk

your thread has been answered here - https://support.mozilla.com/en-US/questions/841462#answer-206284

@olskratch

Please click the Solved It button next to the answer that solved your Firefox support issue, it appears when you are logged in, so this thread gets marked as Solved to help other users who may have this same problem.

Cor El ... thank you for the simple fix: the tools -> general et al

my new system and Firefox updates didn't include this feature REGARDLESS that it offered the "restore previsous sessions" option.

History and select previous session ... did not work.

thanks!