If the site is "blocked" by a security warning (e.g., "Your connection is not secure"): How to Unblock Websites in Firefox - Media Pantheon, Inc.
If a site is blocked by your ISP or Government, use a (like ZenMate or TunnelBear) to change your IP address. Parental Controls:
How To Unblock A Site In Firefox Instant
If the site is "blocked" by a security warning (e.g., "Your connection is not secure"): How to Unblock Websites in Firefox - Media Pantheon, Inc.
If a site is blocked by your ISP or Government, use a (like ZenMate or TunnelBear) to change your IP address. Parental Controls: how to unblock a site in firefox