I think their is no way to get it back. If you had turned on the Firefox sync then you can login with the same account and sync to get all your Firefox addons and bookmarks back.

Look on your desktop. Do you see a folder called; Old Firefox?

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

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

Note that it is usually best to reinstall extensions in the new profile instead of copying them form the "Old Firefox Data" folder on the desktop, but you can at least see which extensions you previously had installed. That will allow them to initialize properly in your current profile.

Did you get the notification that Firefox is slow?

• https://support.mozilla.org/kb/firefox-takes-long-time-start-up
• https://support.mozilla.org/kb/firefox-health-report-says-your-browser-is-slow