Original post is here: eklausmeier.goip.de
Assume three computers A, B, and C. A can connect to B via ssh, but A cannot connect to C, but B can connect to C.
1A -> B -> C
On A open ssh as SOCKS-server with
1ssh -N -D 9020 user@B
Now on A one can use
1brave --proxy-server="socks5://localhost:9020"
The browser will then show up as if directly surfing on B thereby circumventing the limitations on A.
Instead of the brave browser, one can use Chromium, or Firefox. Option "-N": Do not execute a remote command.
See How to Set up SSH SOCKS Tunnel for Private Browsing, or SOCKS.