Open a new tab or window. type about:support in the address box and press enter. Or Press the <Alt> or <F10> key to bring up the tool bar. Then Help > Troubleshooting Information.

Under the page logo on the left side you will see Application Basics. Under this find Profile Folder. To it’s right press the button Show Folder. This will open your file browser to the current Firefox profile. Enter the bookmarkbackups folder. This is where Firefox makes backups of your bookmarks. Look for the file you want to restore (check the time / date). Right click on that file and select Copy. Now go back to the parent folder where you started. Right click in the folder and select Paste. Close FireFox. Rename the file bookmarks.html by adding .old to it. The file you just pasted here, rename it to bookmarks.html. After you are done, restart Firefox.

These can't get your data back, but will help in the future.

These add-ons can be a great help by backing up and restoring Firefox

FEBE (Firefox Environment Backup Extension) {web link} FEBE allows you to quickly and easily backup your Firefox extensions, history, passwords, and more. In fact, it goes beyond just backing up -- It will actually rebuild your saved files individually into installable .xpi files. It will also make backup of files that you choose.

OPIE {web link} Import/Export extension preferences

Do you have a Windows.old folder?

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