The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

How are you closing that window? Are you using the close X on the title bar?

It is possible that you have multiple pages set as the start page and that one opens in the sidebar.

Opening in the sidebar is the default for bookmarks that are created via a link or button on a website.

You can check the Properties of a bookmark via the right-click context menu in the sidebar (Ctrl+B; Cmd+B on Mac).

In the Bookmarks Manager (Bookmarks > Show All Bookmarks) you can click the More button in the Details pane at the bottom right.

Make sure that "Load this bookmark in the sidebar" is not selected.

You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox Profile Folder that store session data.

Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox Profile Folder.

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost, so you will have to create them again (make a note or bookmark them).

• http://kb.mozillazine.org/Multiple_profile_files_created

OK, a big apology. I meant Thunderbird, not Firefox. Anyway, I reset Thunderbird and solved the problem of two exact windows opening. However, all my local folders have disappeared. Is there a way to get them back? Thanks

If you reset Firefox or Thunderbird then a new profile is created and some of your data (bookmarks, passwords, cookies, form data) is automatically imported and your current profile will be moved to the desktop (Old Firefox/Thunderbird Data).

You can recover more data from the old profile (be cautious with doing that).

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Thunderbird
• http://kb.mozillazine.org/Category:Thunderbird

See also the Thunderbird support forums.

• http://forums.mozillazine.org/viewforum.php?f=39

• https://support.mozillamessaging.com/home
• https://getsatisfaction.com/mozilla_messaging/products/mozilla_thunderbird

Cor-el: Thanks for the info. I used:

http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Thunderbird

and was able to install an add-on and import all my local folders. I appreciate your help.

You're welcome