OpenSSH supports dynamic port forwarding (SOCKS tunnels specified via a subset of the SOCKS protocol) through a remote SSH server that allows the user to create a local SOCKS proxy.
The proxies configuration in Firefox can be toggled between "No Proxy" and "Manual proxy configuration" without affecting the proxy configuration details.
Windows SSH SOCKS5 Proxy
PuTTY is a Win32 SSH client that also supports local creation of SOCKS (dynamic) tunnels through remote SSH servers.
PuTTY Win32 SSH could be used as the client on a Windows machine with a similar Firefox configuration.
More Information
Definitions
SOCKS
SOCKet Secure (SOCKS) is an Internet protocol that routes network packets between a client and server through a proxy server. SOCKS5 additionally provides authentication so only authorized users may access a server.
OpenSSH
OpenBSD Secure Shell is a set of computer programs providing encrypted communication sessions over a computer network using the SSH protocol.
SSH
Secure Shell (SSH) is a cryptographic network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that connects, via a secure channel over an insecure network, a server and a client (running SSH server and SSH client programs, respectively). The protocol specification distinguishes two major versions that are referred to as SSH-1 and SSH-2. The encryption used by SSH is intended to provide confidentiality and integrity of data over an unsecured network, such as the Internet.
Intranet
A computer network that uses Internet Protocol technology to share information, operational systems, or computing services within an organization.
Internet
A global network of networks that consists of millions of private, public, academic, business, and government networks, that are linked by a broad array of electronic, wireless and optical networking technologies using the standard Internet protocol suite.