You can try creating a new clean profile, according to the directions found in this support page.

That should likely solve your problem.

Do you remember what files you copied?

You can copy specific files with Firefox closed to the current profile folder to recover personal data stored in the file.

• http://kb.mozillazine.org/Profile_folder_-_Firefox

Note that you should be cautious with copying SQLite database files if you previously had problems.

• bookmarks and history: places.sqlite
• bookmark backups: compressed .jsonlz4 backups in the bookmarkbackups folder
• cookies.sqlite for the cookies
• formhistory.sqlite for saved form data
• logins.json and key3.db (decryption key) for Passwords saved in the Password Manager
• cert8.db and possibly cert_override.txt for (intermediate) certificates stored in the Certificate Manager
• persdict.dat for words you added to the spelling checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other Site Preferences
• sessionstore.js for open tabs and pinned tabs