That grey padlock with the red slash is an indication for a partially secure connection or a mixed-content connection - that is, HTTPS along with HTTP. https://support.mozilla.org/en-US/kb/how-do-i-tell-if-my-connection-is-secure#w_gray-padlock-with-red-strikethrough Also - https://blog.mozilla.org/tanvi/2013/04/10/mixed-content-blocking-enabled-in-firefox-23/ Typical situation for a router, as the 'standards' for HTTPS connections were changed back in Firefox 23, and Firefox is more picky that other browsers. Beyond 'flashing' an updated file to the ROM in that router there isn't a real way to 'fix' that issue. ''Be thankful that you aren't blocked completely as has happens with some routers.'' https://support.mozilla.org/en-US/kb/mixed-content-blocking-firefox "No fix" beyond disabling mixed content blocking which will affect everywhere you go on the internet. Bottom line is you know where you are going, another device on the LAN, so just ignore that indicator when accessing your router.