I'm sorry you didn't have a good experience, however, the official LinkChecker you can download here has zero malware. I've noticed other non-Mozilla websites host extensions, modify them with malware, and make them available for download under the same name.
Please re-download this extension from here and try it again. If the problem persists it may be a bug. Otherwise, I pride myself on my extensions and would never stoop to malware. Feel free to email me directly anytime at email@example.com if you want help troubleshooting.