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Close Firefox. In Finder, hold down Option key, click on Go menu and select Library. Open Mozilla folder, Firefox folder and you will see Profiles folder. You have to delete the corrupted profile from that folder and then copy/move the working one from desktop to this Profiles folder. Then open Firefox app. Does that work ?
If you don't see Profiles folder in that location, then in Finder, hold down Option key, click on Go menu and select Library. Open Application Support folder, open Firefox and you will see the Profiles folder here.
Please let me know if that didn't work, so I will continue to help you