I think this problem is caused by older router firmware that doesn't support IPv6 addresses. If your router has an update available, that would be the best approach: https://www.reddit.com/r/firefox/comments/hmc3t0/google_search_forcing_captcha_dialog_6to4_tunnel/ If not, you could try disabling Firefox from using IPv6 addresses: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button accepting the risk. (2) In the search box in the page, type or paste '''ipv''' and pause while the list is filtered ''Experiment #1:'' (3) Double-click the '''network.dns.ipv4OnlyDomains''' preference to display an editing field, and enter ''www.google''.''com'' (or your actual Google search site) then press Enter or click the blue check mark button to save the change. You may need to clear cache to make sure Firefox requests a new address: [[How to clear the Firefox cache]] (this should be limited to cache and not include cookies/history) ''Experiment #2 (if #1 doesn't work):'' (4) Double-click the '''network.dns.disableIPv6''' preference to switch the value from false to true (You may need to clear cache to make sure Firefox requests a new address) Does that work? More info on about:config: [[Configuration Editor for Firefox]].