Rated 3 out of 5 stars
Although I believe this is a useful tool, I found that on the first page I checked, Link Checker reported a link as valid. However, clicking on link takes one to a different page reported as malware. Copying and pasting the link also gives a bad link. So use LinkChecker with caution.
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 firstname.lastname@example.org if you want help troubleshooting.