If you are using an untrusted network such as an open WiFi network but want all of your traffic (even non-HTTPS connections) to be protected then you can use an ssh server as a SOCKS proxy and have all of your traffic secured using the ssh tunnel.
The switch to use is -D and specify a port number:
ssh -D 9999 chris@mytrustedsshserver.com
Then set up Firefox to use the SOCKS proxy:
Preferences->Advanced->Network->Settings->Manual proxy configuration:
SOCKS Host: 127.0.0.1 Port: 9999
Then use Firefox advanced settings to use the DNS server of your ssh server:
enter about:config in the firefox address bar
type "socks" into the search filter
double click the preference network.proxy.socks_remote_dns to set it to true