Tunneling Connections From a Local Host to a Server, While the Server use a proxy.pac to access the internet

Question

I get access to part of the Internet by ssh login a server, like:

ssh -D 9999 -C user@server

Then set sock proxy on browser 127.0.0.1:9999

The server is behind a firewall. On the server I can access the Internet using a 'proxy.pac' file with username and password

The problem is: can I ssh to the server while having the server use the proxy at the same time?

Can this be done in Python (the only program language I know a little bit)?

Any words will help. Thanks!