The Old Firefox Data folder is created when Firefox's Refresh feature runs. You can read more about that feature in this article: Refresh Firefox - reset add-ons and settings.

The most common reason it might run is if Firefox says it is running slowly and offers the option to speed it up by restoring some default settings. If you click that button, then Refresh happens.

When you start your Firefox now, does it seem to be back to its default settings (with your bookmarks intact, hopefully)?

Do you want to "roll back" the refresh? There's no one-click way to do that, but here is a procedure to revert to your pre-Refresh data. It takes 5 minutes, but that may be faster than recovering individual files and loading those into your new profile.

Check inside the "Old Firefox Data" folder that Refresh adds to your desktop for a folder with a semi-randomized name. If there's only one, that probably has your old settings and add-ons. If there's more than one, you'll want to work with the one that was updated most recently.

Once you have identified the profile folder you want to restore, here is my suggested "old profile resurrection procedure":

Overview

These are the steps described in more detail below:

1. Create a new Firefox profile
2. Remove everything from that new profile folder
3. Copy in everything from the old profile folder

Create a new Firefox profile (Windows)

Exit Firefox completely, and then start up in the Profile Manager by pasting the following into the Start menu search box, or the Start > Run dialog, and pressing Enter:

firefox.exe -P

Note: Any time you want to switch profiles, exit Firefox and return to this dialog.

Click the Create Profile button, assign a name like OldSettings, and skip the option to change the folder location. Then select that new profile in the dialog and start Firefox.

Open the New Profile folder in Windows Explorer

Firefox in the new profile should look like a factory fresh installation. Open the Troubleshooting Information page using either:

• "3-bar" menu button > "?" button > Troubleshooting Information
• Help menu > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table, click the "Show Folder" button. Firefox will launch your brand new profile folder in Windows Explorer.

Leaving that folder open, switch back to Firefox, and Exit using either:

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

When Firefox closes, the profile folder should be front and center, or you can activate it using the Task bar.

Copy Old Data in Place of New

In that new profile folder you just popped open -- NOT the one on your desktop -- select all the contents (you can use Ctrl+a) and delete (you can press the Delete key on the keyboard).

Leaving that window open, open or switch over to your Old Firefox Data folder. Drill down into your old profile folder. At this level you should see a folder named bookmarkbackups among other things.

Select everything (Ctrl+a) and Copy (either right-click > Copy or Ctrl+c).

Switch to the empty new profile folder in other window and Paste (either right-click > Paste or Ctrl+v). This may take a minute since some of the files are large.

Start Firefox

Firefox should start up in that "new" profile with the resurrected old profile data. Success?

When you Refresh/Reset Firefox then a new profile is created and some personal data (bookmarks, history, cookies, passwords, form data) is automatically imported. The current profile folder will be moved to an "Old Firefox Data" folder on the desktop. Installed extensions and other customizations (toolbars, prefs) that you have made are lost and need to be redone.

It is possible to recover data from the "Old Firefox Data" folder on the desktop, but be cautious not to copy corrupted files to avoid carrying over problems.

If you have an "Old Firefox Data" folder on the desktop then you can recover some personal data from a recent profile in that folder. You can copy/transfer files like these to your current Firefox profile folder.

• bookmarks/history: backups in the bookmarkbackups folder and possibly places.sqlite if you really need the history
• other SQLite files like cookies.sqlite (cookies) and formhistory.sqlite (saved form data)
• logins.json and key3.db (decryption key) for Passwords saved in the Password Manager
• permissions.sqlite and possibly content-prefs.sqlite for Permissions and Site Preferences
• cert8.db for stored intermediate certificates (Certificate Manager)
• sessionstore.js for open tabs and pinned tabs and tab groups

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

See also:

• https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox