Sign up for a reputable VPN service like Mullvad, ProtonVPN, or ExpressVPN. Download and install their application, connect to a server in an allowed location, then open Firefox—all your browsing will be unblocked.
If Firefox says "Hmm. We’re having trouble finding that site," the site might be blocked at the operating system level, not by Firefox. This is common in workplaces or parental control setups. how to unblock a site in firefox
If you frequently visit developer sites or internal pages that trigger false positives, you can disable this security feature entirely: Sign up for a reputable VPN service like