I can think of two possibilities:

(1) Firefox is crashing during shutdown and doing an automatic session recovery at startup. To give Firefox the best chance of shutting down normally, use the Exit command on the menu (not the "red X" button). Either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

You also can change what Firefox does after a crash so that instead of recovering automatically, it gives you the option. I'll put the steps for that at the end in case you're interested.

(2) An optional settings file named user.js contains a command to restore your previous session just once. Firefox uses the settings in that file at startup to override your saved preferences from the previous session, so just once becomes every startup.

You can check for this optional file, and remove it if you find it, using the steps in this article: How to fix preferences that won't save (there's a specific section on user.js files).

Windows normally hides the .js extension, as well as various others. To work with files as accurately as possible, I suggest showing all extensions. This Microsoft support article has the steps: http://windows.microsoft.com/en-us/wi.../show-hide-file-name-extensions.

Does either of those seem relevant?

One way to diagnose whether Firefox thinks it is crashing at shutdown is to set a different post-crash startup behavior. Rather than trying to restore automatically, Firefox will display a list of windows and tabs you had open before and ask whether you want to restore them or start a new session. Here's how you get to that, if you want to try it:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) Double-click the browser.sessionstore.max_resumed_crashes preference and change its value from 1 to 0 (zero) and click OK

Please be careful not to change other session restore settings so that you can preserve this option for when you really need it.

Thank you for your valuable information. Out of 2 possibilities 1st one did not work. Exiting Firefox by pressing "power" button or "File>Exit" has the same result.

2nd option solved the problem. I just commented the line “user_pref("browser.sessionstore.resume_session_once", true);” in user.js file.

Thank you once again...