If removing the files from these folders resolves the issue, quit Safari again and gradually put back files until you find the one causing the issue:
Open the Trash and select one of the files you removed. Chose File > Put Back. The file returns to its folder.
Open Safari and see if the issue returns.
If the issue returns, you've identified the add-on causing the issue. Avoid using it or contact its maker for an updated version.
If the issue doesn't return, quit Safari and put back another file.