That's due to "matches" being set to "all_urls". That's required for this add-on to work on all sites.

See:
* https://developer.chrome.com/extensions/match_patterns
* https://github.com/danielnixon/link-fixer/blob/master/manifest.json#L15

Feel free to audit the source at https://github.com/danielnixon/link-fixer

See also https://blog.mozilla.org/addons/2018/02/01/understanding-extension-permission-requests/