This could happen if you used the Reset feature, maybe if Firefox suggested it to speed up the startup time. A Reset creates a folder on your desktop named "Old Firefox Data". Is there such a folder?

At this time, Your System Details shows;

Extensions

Troubleshooter 1.1a (troubleshooter@mozilla.org) Avast Online Security 10.0.2204.148 (wrc@avast.com) (Inactive)

Yes there is a folder "Old Firefox Data" on my DeskTop What to do now ?

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

Your active Firefox profile folders are hidden. To access them, you can use this approach (from inside Firefox). Either:

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

In the first table on the page, click the "Show in Finder" button. This should launch a new Finder window listing your settings files and various subfolders.

If you navigate up one level to the Profiles folder and copy your oldest profile folder (from Old Firefox Data) here, Firefox won't be able to find it automatically, You will need to navigate up another level to the Firefox folder and edit profiles.ini with the name (Path) of the freshly restored folder.