Your old Firefox profile should be on your desktop in a folder named "Old Firefox Data."

Recover important data from an old profile using the following procedure: https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile#w_copying-files-between-profile-folders

What problem did you have with your previous profile folder that you decided to reset Firefox?

For certificates you would need the cert8.db file.
Copying an old prefs.js file is less recommended and it is probably better to redo all changes in Options and make other changes on the about:config page if you did make specific changes previously yourself.