How to connect with Pidgin to Facebook-chat and Google Talk when XMPP port 5222 is blocked?

It turns out this is thought for and one can use the common ports (80 for HTTP and 443 for HTTPS), but not all combinations work.

For Pidgin on Ubuntu 12.04, but it would likely work with different wording for other clients such as Miranda, Psi, or Gajim. Go to Accounts>Manage Accounts (or press CTRL+A), pick your Facebook or GTalk account and go to the advanced tab. Fill in as follows:

(For Facebook)

• Connection security: Require encryption
• Connect port: 443
• Connect server: chat.facebook.com

(For Google Talk)

• Connection security: Use old-style SSL
• Connect port: 443
• Connect server: talk.google.com

Leave "Allow plaintext auth [...]" and other fields unfilled ("Show Custom Smileys" is up to you).

Now you should connect just fine.