There are some fight between the ISP and the dominate Phone/DSL distributor. The result is that I have to use the 56k connection temporary.

I use squid to improve the browsing performance. It's great, but I get a small problem. When I type something in google's search bar, it return a ERROR:The requested URL could not be retrieved

that mean when I type "google" in firefox's address, squid return a page that the dns server cannot resolv the dns request. However, it doesn't return an error that firefox understand hence firefox doesn't do a search.

How to correct it?

The nature of the proxy will always cause that and trying to change the behaviour would probably result in odd behaviour. A possible solution would be to edit the squid failure page to redirect you to the google search after a few seconds.