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.
You can use "Firefox > History > Restore Previous Session" to get the previous session.
There is also a "Restore Previous Session" button on the default about:home Home page.

Another possibility is to use:

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

"Firefox > History > Restore Previous Session"

this is always greyed out... and the only way i managed not to loose all my tabs every time i have to close FF, is using in options > general: When Firefox Starts": "Show my windows and tabs from last time. yep, i probably was with wrong contact lenses last night, because i didn't saw this... this still feels a little dumb since it doesn't give me the option to save or not to save (there is the question! lol) the open tabs... i'm a litle hardcore when using tabs (i love to stress FF) because most of the times, i'm working on multiple subject/searches. I tend to have 10+ tabs open (past record was 42).

• Make sure that you not run Firefox in Permanent Private Browsing - Use Firefox without saving history mode.

• You enter Private Browsing mode if you select: Tools > Options > Privacy > History: Firefox will: "Never Remember History"
• To see all History and Cookie settings, choose: Tools > Options > Privacy, choose the setting Firefox will: Use custom settings for history
• Uncheck: [ ] "Permanent Private Browsing mode"

i'm not in permanent private browsing, but thank you for that enlightenment.

i'm using "When Firefox Starts": "Show my windows and tabs from last time" ... at least i'll have my last open tabs every time i open FF...

Thank you for you answers!

I'm having the same issues as quimkaos - if I don't go to "When Firefox Starts" and change it to "Show my windows and tabs from last time" EVERY TIME I get ready to close Firefox it won't save the tabs next time I open it. Why isn't there an option to save "Show my windows and tabs from last time"?

Try this, I had the problem before and found it in the forums and it worked for me. It should work to enable Firefox asking if you want to quit or quit and save tabs when you exit.

  1. Type about:config into the location bar and press enter
  2. Accept the warning message that appears, you will be taken to a list of preferences
  3. Locate the preference browser.tabs.warnOnClose, if its value is set to false, double-click on it to change its value to true
  4. Repeat this for these 3 preferences browser.warnOnQuit, browser.warnOnRestart and browser.showQuitWarning

i'm going to try this tomorrow, but seems good from were i'm looking

Thanks agwarfel - this seems to work just fine.

Tools > Options > General > Startup: "When Firefox Starts": "Show my windows and tabs from last time"...............................................THIS WORKED FOR ME.

Only wish I found this suggestion about 4 hours ago!!!!

"Only wish I found this suggestion about 4 hours ago!!!! "

i'm still looking....

agwarfel solution maybe working on 3x versions but not in version 4x... and now i'm getting to the point of: is Mozilla foundation in love with MS corporation? 1st the so called "firefox" MICROSOFT menu, then the we don't care for testing my MS stuff under linux (not even ubuntu) and i can imagine now what have been done for mac...

then something stupid appends... a basic function like asking if you want to keep your tabs or not is not relevant... users don't matter... we are open source!

please mozilla sell you selfs for once to MS and don't bother since other browser like opera, safari or chrome will do better than you..